问题1.找到以下方程式的一般解：
(i)正弦θ = 1/2
解决方案：
We are given,
=> sin θ = 1/2
=> sin θ = sin π/6
We know if sin θ = sin a, the general solution is given by, θ = nπ + (−1)n a; n ∈ Z.
=> θ = nπ + (−1)n (π/6) ; n ∈ Z
(ii)cosθ = −√3 / 2
解决方案：
We are given,
=> cos θ = −√3/2
=> cos θ = cos (π + π/6)
=> cos θ = cos (7π/6)
We know if cos θ = cos a, the general solution is given by, θ = 2nπ ± a ; n ∈ Z.
=> θ = 2nπ ± (7π/6) ; n ∈ Z
(iii) cosecθ= −√2
解决方案：
We are given,
=> cosec θ = −√2
=> 1/sin θ = −√2
=> sin θ = −1/√2
=> sin θ = −sin (π/4)
As sin (−θ) = − sin θ, we have,
=> sin θ = sin (−π/4)
We know if sin θ = sin a, the general solution is given by, θ = nπ + (−1)n a ; n ∈ Z.
=> θ = nπ + (−1)n+1 (π/4) ; n ∈ Z
(iv)秒θ =√2
解决方案：
We are given,
=> sec θ = √2
=> 1/sec θ = √2
=> cos θ = 1/√2
=> cos θ = cos π/4
We know if cos θ = cos a, the general solution is given by, θ = 2nπ ± a ; n ∈ Z.
=> θ = 2nπ ± (π/4) ; n ∈ Z
(v)tanθ = −1 /√3
解决方案：
We are given,
=> tan θ = −1/√3
=> tan θ = −tan (π/6)
As tan (−θ) = − tan θ, we have,
=> tan θ = tan (−π/6)
We know if tan θ = tan a, the general solution is given by, θ = nπ + a ; n ∈ Z.
=> θ = nπ − (π/6) ; n ∈ Z
(vi)√3秒θ = 2
解决方案：
We are given,
=> √3 sec θ = 2
=> √3 (1/cos θ) = 2
=> cos θ = √3/2
=> cos θ = cos (π/6)
We know if cos θ = cos a, the general solution is given by, θ = 2nπ ± a; n ∈ Z.
=> θ = 2nπ ± (π/6) ; n ∈ Z
问题2。找到以下方程的一般解：
(i)罪2θ =√3/ 2
解决方案：
We are given,
=> sin 2θ = √3/2
=> sin 2θ = sin (π/3)
We know if sin θ = sin a, the general solution is given by, θ = nπ + (−1)n a; n ∈ Z.
=> 2θ = nπ + (−1)n (π/3)
=> θ = nπ/2 + (−1)n (π/6) ; n ∈ Z
(ii)cos 3θ = 1/2
解决方案：
We are given,
=> cos 3θ = 1/2
=> cos 3θ = cos (π/3)
We know if cos θ = cos a, the general solution is given by, θ = 2nπ ± a; n ∈ Z.
=> 3θ = 2nπ ± (π/3)
=> θ = 2nπ/3 ± (π/9) ; n ∈ Z
(iii)正弦9θ =正弦θ
解决方案：
We are given,
=> sin 9θ = sin θ
=> sin 9θ – sin θ = 0
=> 2 cos 5θ sin 4θ = 0
=> cos 5θ = 0 or sin 4θ = 0
We know, if cos θ = 0, then θ = (2n+1)π/2 and if sin θ = 0, then θ = nπ where n ∈ Z.
=> 5θ = (2n+1)π/2 or 4θ = nπ
=> θ = (2n+1)π/10 or θ = nπ/4, n ∈ Z
(iv)sin2θ= cos3θ
解决方案：
We are given,
=> sin 2θ = cos 3θ
=> cos 3θ = sin 2θ
=> cos 3θ = cos (π/2 − 2θ)
We know if cos θ = cos a, the general solution is given by, θ = 2nπ ± a ; n ∈ Z.
=> 3θ = 2nπ ± (π/2 − 2θ)
=> 3θ = 2nπ + π/2 − 2θ or 3θ = 2nπ − π/2 + 2θ
=> 5θ = 2nπ + π/2 or θ = 2nπ − π/2
=> 5θ = (4n+1) (π/2) or θ = (4n−1) (π/2)
=> θ = (4n+1)π/10 or θ = (4n−1)π/2, n ∈ Z
(v)tanθ+ cot2θ= 0
解决方案：
We are given,
=> tan θ + cot 2θ = 0
=> cot 2θ = − tan θ
=> tan 2θ = − cot θ
=> tan 2θ = − tan (π/2 − θ)
As tan (−θ) = − tan θ, we have,
=> tan 2θ = tan (θ − π/2)
We know if tan θ = tan a, the general solution is given by, θ = nπ + a ; n ∈ Z.
=> 2θ = nπ + θ − π/2
=> θ = nπ − π/2 ; n ∈ Z
(vi)tan3θ=婴儿床θ
解决方案：
We are given,
=> tan 3θ = cot θ
=> tan 3θ = tan (π/2 − θ)
We know if tan θ = tan a, the general solution is given by, θ = nπ + a ; n ∈ Z.
=> 3θ = nπ + π/2 − θ
=> 4θ = nπ + π/2
=> θ = nπ/4 + π/8 ; n ∈ Z
(vii)tan2θtanθ= 1
解决方案：
We are given,
=> tan 2θ tan θ = 1
=> tan 2θ = cot θ
=> tan 2θ = tan (π/2 − θ)
We know if tan θ = tan a, the general solution is given by, θ = nπ + a ; n ∈ Z.
=> 2θ = nπ + π/2 − θ
=> 3θ = nπ + π/2
=> θ = nπ/3 + π/6 ; n ∈ Z
(viii)tanmθ+子床nθ= 0
解决方案：
We are given,
=> tan mθ + cot nθ = 0
=> sin mθ/cos mθ + cos nθ/sin nθ = 0
=> sin mθ sin nθ + cos nθ cos mθ = 0
=> cos (m−n)θ = 0
We know, if cos θ = 0, then θ = (2k+1)π/2 where k ∈ Z.
=> (m−n)θ = (2k+1)π/2
=> θ = (2k+1)π/2(m−n) ; n ∈ Z
(ix)tanpθ= cotqθ
解决方案：
We are given,
=> tan pθ = cot qθ
=> tan pθ = tan (π/2 − qθ)
We know if tan θ = tan a, the general solution is given by, θ = nπ + a ; n ∈ Z.
=> pθ = nπ + π/2 − qθ
=> (p + q)θ = (2n+1)π/2
=> θ = (2n+1)π/2(p + q) ; n ∈ Z
(x)罪2x + cos x = 0
解决方案：
We are given,
=> sin 2x + cos x = 0
=> cosx = − sin 2x
=> cos x = cos (π/2 + 2x)
We know if cos θ = cos a, the general solution is given by, θ = 2nπ ± a ; n ∈ Z.
=> x = 2nπ ± (π/2 + 2x)
=> x = 2nπ + π/2 + 2x or x = 2nπ − π/2 − 2x
=> x = −(4n+1)π/2 or 3x = (4n−1)π/2
=> x = −(4n+1)π/2 or 3x = (4n−1)π/2
=> x = (4m−1)π/2, where m = −n or x = (4n−1)π/6, n ∈ Z
(xi)sinθ= tanθ
解决方案：
We are given,
=> sin θ = tan θ
=> sin θ = sin θ/cos θ
=> sin θ (cos θ − 1) = 0
=> sin θ = 0 or cos θ = 1
=> sin θ = 0 or cos θ = cos 0
We know, if cos θ = 0, then θ = (2n+1)π/2 and if sin θ = 0, then θ = nπ where n ∈ Z.
=> θ = nπ or θ = 2nπ, n ∈ Z
(xii)罪3x + cos 2x = 0
解决方案：
We are given,
=> sin 3x + cos 2x = 0
=> cos 2x = −sin 3x
=>cos 2x = cos (π/2 + 3x)
We know if cos θ = cos a, the general solution is given by, θ = 2nπ ± a ; n ∈ Z.
=> 2x = 2nπ ± (π/2 + 3x)
=> 2x = 2nπ + π/2 + 3x or 2x = 2nπ − π/2 − 3x
=> −x = 2nπ + π/2 or 5x = 2nπ − π/2
=> x = 2mπ − π/2, where m = −n or x = (2nπ − π/2)/5
=> x = (4m−1)π/2, where m = −n or x = (4n−1)π/10, n ∈ Z
问题3.求解以下方程式：
(i)sin 2θ -cosθ= 1/4
解决方案：
We have,
=> sin2 θ − cos θ = 1/4
=> 1 − cos2 θ − cos θ = 1/4
=> cos2 θ + cos θ − 3/4 = 0
=> 4cos2 θ + 4cos θ − 3 = 0
=> 4cos2 θ + 6cos θ − 2cos θ − 3 = 0
=> 2cos θ (2cos + 3) − (2cos θ + 3) = 0
=> (2cos θ − 1) (2cos θ + 3) = 0
=> cos θ = 1/2 or cos θ = −3/2
Ignoring cos θ = −3/2 as −1 ≤ cosθ ≤ 1. So, we have, cos θ = 1/2.
=> cos θ = cos π/3
=> θ = 2nπ ± π/3 ; n ∈ Z
(ⅱ)2COS 2θ – 5cosθ+ 2 = 0
解决方案：
We are given,
=> 2cos2 θ − 5cos θ + 2 = 0
=> 2cos2 θ − 4cos θ − cos θ + 2 = 0
=> 2cos θ (cos θ − 2) − (cos θ − 2) = 0
=> (2cos θ − 1) (cos θ − 2) = 0
=> cos θ = 1/2 or cos θ = 2
Ignoring cos θ = 2 as −1 ≤ cosθ ≤ 1. So, we have, cos θ = 1/2.
=> cos θ = cos π/3
=> θ = 2nπ ± π/3 ; n ∈ Z
(iii) 2罪2 x +√3cosx +1 = 0
解决方案：
We are given,
=> 2sin2 x + √3cos x + 1 = 0
=> 2 (1 − cos2 x) + √3cos x + 1 = 0
=> 2cos2 x − √3cos x − 3 = 0
=> 2cos2 x − 2√3cos x + √3cos x − 3 = 0
=> 2cosx (cos x − √3) + √3(cos x − √3) = 0
=> (2cosx + √3) (cos x − √3) = 0
=> x = −√3/2 or x = √3
Ignoring cos x = √3 as −1 ≤ cosθ ≤ 1. So, we have, cos x = −√3/2.
=> cos x = − cos π/6
=> cos x = cos (π − π/6)
=> cos x = cos (5π/6)
=> x = 2nπ ± 5π/6 ; n ∈ Z
(iv)4sin 2θ -8cosθ+1 = 0
解决方案：
We are given,
=> 4sin2 θ − 8cos θ + 1 = 0
=> 4 (1 − cos2 θ) − 8cos θ + 1 = 0
=> 4 cos2 θ + 8 cos θ − 5 = 0
=> 4 cos2 θ + 10 cos θ − 2 cos θ − 5 = 0
=> 2cos θ (2cos θ +5) − (2cos θ +5) = 0
=> (2cos θ − 1) (2cos θ +5) = 0
=> cos θ = 1/2 or cos θ = −5/2
Ignoring cos x = −5/2 as −1 ≤ cosθ ≤ 1. So, we have, cos x = 1/2.
=> cos x = cos π/3
=> x = 2nπ ± π/3 ; n ∈ Z
(v)棕褐色2 x +(1 −√3)棕褐色x −√3= 0
解决方案：
We are given,
=> tan2 x + (1 − √3)tan x − √3 = 0
=> tan2 x + tan x − √3tan x − √3 = 0
=> tan x (tan x + 1) − √3 (tan x + 1) = 0
=> (tan x − √3) (tan x + 1) = 0
=> tan x = √3 or tan x = −1
=> tan x = tan π/3 or tan x = −tan π/4
=> tan x = tan π/3 or tan x = tan (−π/4)
=> x = nπ + π/3 or x = nπ − π/4, n ∈ Z
(vi)3 cos 2θ -2√3sinθcosθ-3 sin 2θ = 0
解决方案：
We have,
=> 3 cos2 θ − 2√3 sin θ cos θ − 3 sin2 θ = 0
=> √3 cos2 θ − 2 sin θ cos θ − √3 sin2 θ = 0
=> √3 cos2 θ + sin θ cos θ − 3 sin θ cos θ − √3 sin2 θ = 0
=> cos θ (√3cos θ + sin θ) − √3sin θ (√3cos θ + sin θ) = 0
=> (√3cos θ + sin θ) (cos θ − √3sin θ) = 0
=> tan θ = −√3 or tan θ = 1/√3
=> tan θ = − tan π/3 or tan θ = tan π/6
=> tan θ = tan (−π/3) or tan θ = tan π/6
=> θ = nπ − π/3 or θ = nπ + π/6, n ∈ Z
(vii)cos4θ= cos2θ
解决方案：
We have,
=> cos 4θ = cos 2θ
=> cos 4θ − cos 2θ = 0
=> 2 sin 3θ sin θ = 0
=> sin 3θ = 0 or sin θ = 0
=> 3θ = nπ or θ = nπ
=> θ = nπ/3 or θ = nπ, n ∈ Z
问题4.求解以下方程式：
(i)cosθ+ cos2θ+ cos3θ= 0
解决方案：
We are given,
=> cos 2θ + (cos θ + cos 3θ) = 0
=> cos 2θ + 2cos 2θ cos θ = 0
=> cos 2θ (1 + 2cos θ) = 0
=> cos 2θ = 0 or cos θ = −1/2
=> 2θ = (2n+1)π/2 or cos θ = cos (π − π/3)
=> θ = (2n+1)π/4 or θ = 2nπ ± (2π/3), n ∈ Z
(ii)cosθ+ cos3θ-cos2θ= 0
解决方案：
We are given,
=> cos θ + cos 3θ − cos 2θ = 0
=> 2cos 2θ cos θ − cos 2θ = 0
=> cos 2θ (2cos θ − 1) = 0
=> cos 2θ = 0 or cos θ = 1/2
=> 2θ = (2n+1)π/2 or cos θ = cos π/3
=> θ = (2n+1)π/4 or θ = 2nπ ± (π/3), n ∈ Z
(iii)sinθ+ sin5θ= sin3θ
解决方案：
We are given,
=> sin θ + sin 5θ = sin 3θ
=> 2sin 3θ cos 2θ − sin 3θ = 0
=> sin 3θ (2cos 2θ − 1) = 0
=> sin 3θ = 0 or cos 2θ = 1/2
=> sin 3θ = 0 or cos 2θ = cos π/3
=> 3θ = nπ or 2θ = 2nπ ± (π/3)
=> θ = nπ/3 or θ = nπ ± (π/6), n ∈ Z
(iv)cosθcos2θcos3θ= 1/4
解决方案：
We are given,
=> cos θ cos 2θ cos 3θ = 1/4
=> 2cos θ cos 3θ cos 2θ = 1/2
=> (cos 4θ + cos 2θ) cos 2θ = 1/2
=> (2cos2 2θ − 1 + cos 2θ) cos 2θ = 1/2
=> 2cos3 2θ − cos 2θ + cos2 2θ = 1/2
=> 4cos3 2θ − 2cos 2θ + 2cos2 2θ − 1 = 0
=> 2cos2 2θ (2cos 2θ + 1) − (2cos 2θ + 1) = 0
=> (2cos2 2θ − 1) (2cos 2θ + 1) = 0
=> 2cos2 2θ − 1 = 0 or 2cos 2θ + 1 = 0
=> cos 4θ = 0 or cos 2θ = −1/2
=> 4θ = (2n+1)π/2 or cos 2θ = cos 2π/3
=> θ = (2n+1)π/8 or 2θ = 2nπ ± (2π/3)
=> θ = (2n+1)π/8 or 2θ = nπ ± (π/3), n ∈ Z
(v)cosθ+ sinθ= cos2θ+ sin2θ
解决方案：
We are given,
=> cos θ + sin θ = cos 2θ + sin 2θ
=> cos θ − cos 2θ = sin 2θ − sin θ
=> 2 sin 3θ/2 sin θ/2 = 2 cos 3θ/2 sin θ/2
=> 2 sin θ/2 (sin 3θ/2 − cos 3θ/2) = 0
=> sin θ/2 = 0 or (sin 3θ/2 − cos 3θ/2) = 0
=> θ/2 = nπ or tan 3θ/2 = 1
=> θ = 2nπ or tan 3θ/2 = tan π/4
=> θ = 2nπ or 3θ/2 = nπ ± π/4
=> θ = 2nπ or θ = 2nπ/3 ± π/6, n ∈ Z
(vi)sinθ+ sin2θ+ sin3θ= 0
解决方案：
We are given,
=> (sin θ + sin 3θ) + sin 2θ = 0
=> 2sin 2θ cos θ + sin 2θ = 0
=> sin 2θ (2cos θ + 1) = 0
=> sin 2θ = 0 or 2cos θ + 1 = 0
=> 2θ = nπ or cos θ = −1/2
=> θ = nπ/2 or cos θ = cos 2π/3
=> θ = nπ/2 or θ = 2nπ ± (2π/3), n ∈ Z
(vii)sin x + sin 2x + sin 3x + sin 4x = 0
解决方案：
We are given,
=> sin x + sin 2x + sin 3x + sin 4x = 0
=> (sin x + sin 3x) + (sin 2x + sin 4x) = 0
=> 2 sin 2x cos x + 2 sin 3x cos x = 0
=> 2cos x (sin 2x + sin 3x) = 0
=> (2cos x) (2sin 5x/2) (cos x/2) = 0
=> cos x = 0 or sin 5x/2 = 0 or cos x/2 = 0
=> x = (2n+1)π/2 or 5x/2 = nπ or cos x/2 = 0
=> x = (2n+1)π/2 or x = 2nπ/5 or x/2 = (2n+1)π/2
=> x = (2n+1)π/2 or x = 2nπ/5 or x = (2n+1)π, n ∈ Z
(ⅷ)罪3θ -罪θ= 4 COS 2θ – 2
解决方案：
We are given,
=> sin 3θ − sin θ = 4 cos2 θ − 2
=> 2 cos 2θ sin θ = 2 (2cos2 θ − 1)
=> 2 cos 2θ sin θ = 2 cos 2θ
=> 2 cos 2θ (sin θ − 1) = 0
=> cos 2θ = 0 or (sin θ − 1) = 0
=> 2θ = (2n+1)π/2 or sin θ = 1
=> θ = (2n+1)π/4 or sin θ = sin π/2
=> θ = (2n+1)π/4 or θ = nπ + (−1)n (π/2), n ∈ Z
(ix)sin 2x− sin 4x + sin 6x = 0
解决方案：
We are given,
=> sin 2x− sin 4x + sin 6x = 0
=> 2 sin 4x cos 2x − sin 4x = 0
=> 2 sin 4x (cos 2x − 1) = 0
=> sin 4x = 0 or cos 2x = 1/2
=> 4x = nπ or cos 2x = cos π/3
=> x = nπ/4 or 2x = 2nπ ± (π/3)
=> x = nπ/4 or x = nπ ± (π/6), n ∈ Z
问题5.求解以下方程式：
(i)棕褐色x +棕褐色2x +棕褐色3x = 0
解决方案：
We are given,
=> tan x + tan 2x + tan 3x = 0
=> (tan x + tan 2x) + tan (2x+x) = 0
=> (tan x + tan 2x) + (tan x + tan 2x)/(1 − tan x tan 2x) = 0
=> (tan x + tan 2x) [1 + 1/(1 − tan x tan 2x)] = 0
=> (tan x + tan 2x) (2 − tan x tan 2x) = 0
=> (tan x + tan 2x) = 0 or (2 − tan x tan 2x) = 0
=> tan x = −tan 2x or tan x tan 2x = 2
=> tan x = tan (−2x) or tan x [2tan x/(1−tan2 x)] = 2
=> x = nπ − 2x or 2tan2 x = 2 − tan2 x
=> 3x = nπ or 4tan2 x = 2
=> x = nπ/3 or tan2 x = 1/2
=> x = nπ/3 or tan x = 1/√2 or tan x = −1/√2
=> x = nπ/3 or tan x = tan π/4 or tan x = tan (−π/4)
=> x = nπ/3 or x = nπ + π/4 or x = nπ − π/4
=> x = nπ/3 or x = nπ ± π/4, n ∈ Z
(ii)tanθ+ tan2θ= tan3θ
解决方案：
We are given,
=> tan θ + tan 2θ = tan 3θ
=> (tan θ + tan 2θ) − tan (2θ+θ) = 0
=> (tan θ + tan 2θ) − (tan θ + tan 2θ)/(1 − tan θ tan 2θ) = 0
=> (tan θ + tan 2θ) [1 − 1/(1 − tan θ tan 2θ)] = 0
=> (tan θ + tan 2θ) (−tan θ tan 2θ) = 0
=> (tan θ + tan 2θ) = 0 or −tan θ = 0 or tan 2θ = 0
=> tan θ = tan (−2θ) or tan θ = 0 or tan 2θ = 0
=> θ = nπ − 2θ or θ = nπ or 2θ = nπ
=> θ = nπ/3 or θ = nπ or θ = nπ/2, n ∈ Z
(iii)tan3θ+ tanθ= 2tan2θ
解决方案：
We are given,
=> tan 3θ + tan θ = 2tan 2θ
=> tan 3θ − tan 2θ = tan 2θ − tan θ
=> 2 sin2 θ sin 2θ = 0
=> sin θ = 0 or sin 2θ = 0
=> θ = nπ or θ = nπ/2, n ∈ Z
问题6.求解以下方程式：
(i)sinθ+ cosθ=√2
解决方案：
We are given,
=> sin θ + cos θ = √2
=> (1/√2) sin θ + (1/√2) cos θ = 1
=> sin π/4 sin θ + cos π/4 cos θ = 1
=> cos (θ − π/4) = cos 0
=> θ − π/4 = 2nπ
=> θ = 2nπ + π/4
=> θ = (8n+1)π/4, n ∈ Z
(ii)√3cosθ+ sinθ= 1
解决方案：
We are given,
=> √3 cos θ + sin θ = 1
=> (√3/2) cos θ + (1/2) sin θ = 1/2
=> cos π/6 cos θ + sin π/6 sin θ = 1/2
=> cos (θ − π/6) = cos π/3
=> θ − π/6 = 2nπ ± π/3
=> θ = 2nπ ± π/3 + π/6
=> θ = 2nπ + π/3 − π/6 or θ = 2nπ − π/3 + π/6
=> θ = 2nπ + π/2 or θ = 2nπ − π/6
=> θ = (4n+1)π/2 or θ = (12n−1)π/6, n ∈ Z
(iii)sinθ+ cosθ= 1
解决方案：
We are given,
=> sin θ + cos θ = 1
=> (1/√2) cos θ + (1/√2) sin θ = 1/√2
=> cos π/4 cos θ + sin π/4 sin θ = 1/√2
=> cos (θ − π/4) = cos π/4
=> θ − π/4 = 2nπ ± π/4
=> θ = 2nπ ± π/4 + π/4
=> θ = 2nπ + π/2 or θ = 2nπ, n ∈ Z
(iv)cosecθ= 1 +科特角θ
解决方案：
We are given,
=> cosec θ = 1 + cot θ
=> 1/sin θ = 1 + cos θ/sin θ
=> sin θ + cos θ = 1
=> (1/√2) cos θ + (1/√2) sin θ = 1/√2
=> cos π/4 cos θ + sin π/4 sin θ = 1/√2
=> cos (θ − π/4) = cos π/4
=> θ − π/4 = 2nπ ± π/4
=> θ = 2nπ ± π/4 + π/4
=> θ = 2nπ + π/2 or θ = 2nπ, n ∈ Z
(v)(√3− 1)cosθ+(√3+1)sinθ= 2
解决方案：
We are given,
=> (√3 − 1) cos θ + (√3 + 1) sin θ = 2
=> (√3 − 1) cos θ/2√2 + (√3 + 1) sin θ/2√2 = 2
=> sin (θ + tan-1 (√3 − 1)/(√3 + 1)) = sin π/4
=> θ = 2nπ + π/3 or θ = 2nπ − π/6, n ∈ Z
问题7：求解以下方程式：
(i)婴儿床x +棕褐色x = 2
解决方案：
We are given,
=> cot x + tan x = 2
=> cos x/sin x + sin x/cos x = 2
=> (cos2 x + sin2 x)/sin x cos x = 2
=> 2 sin x cos x = 1
=> sin 2x = 1
=> sin 2x = sin π/2
=> 2x = (2n+1)π/2
=> x = (2n+1)π/4, n ∈ Z
(ii)2 sin 2θ = 3 cosθ，0≤θ≤2π
解决方案：
We are given,
=> 2 sin2 θ = 3 cos θ
=> 2 (1 − cos2 θ) − 3 cos θ = 0
=> 2 cos2 θ + 3 cos θ − 2 = 0
=> 2 cos2 θ + 4 cos θ − cos θ − 2 = 0
=> 2 cos θ (cos + 2) − (cos θ + 2) = 0
=> (2 cos θ − 1) (cos θ + 2) = 0
=> cos θ = 1/2 or cos θ = −2
Ignoring cos θ =−2 as −1 ≤ cos θ ≤ 1. So, we have, cos θ = 1/2.
=> cos θ = cos π/3
=> θ = 2nπ ± π/3, n ∈ Z
(iii)秒x cos 5x +1 = 0，0≤x≤π/ 2
解决方案：
We are given,
=> sec x cos 5x +1 = 0
=> (cos5x + cos x)/cos x = 0
=> 2 cos 3x cos 2x = 0
=> cos 3x = 0 or cos 2x = 0
=> 3x = (2n+1)π/2 or 2x = (2n+1)π/2
=> x = (2n+1)π/6 or x = (2n+1)π/4, n ∈ Z
(iv)5 cos 2θ + 7 sin 2θ -6 = 0
解决方案：
We are given,
=> 5 cos2 θ + 7 sin2 θ − 6 = 0
=> 5 (1 − sin2 θ) + 7 sin2 θ − 6 = 0
=> 2 sin2 θ+ 5 − 6 = 0
=> 2 sin2 θ = 1
=> sin θ = ±(1/√2)
=> θ = nπ ± π/4, n ∈ Z
(v)sin x − 3 sin 2x + sin 3x = cos x − 3 cos 2x + cos 3x
解决方案：
We are given,
=> sin x − 3 sin 2x + sin 3x = cos x − 3 cos 2x + cos 3x
=> (sin x + sin 3x) − 3 sin 2x − (cos x + cos 3x) + 3 cos 2x = 0
=> 2 sin 2x cos x − 3 sin 2x − 2 cos 2x cos x + 3 cos 2x = 0
=> sin 2x (2 cos x − 3) − cos 2x (2 cos x − 3) = 0
=> (sin 2x − cos 2x) (2 cos x − 3) = 0
=> sin 2x = cos 2x or cos x = 3/2
Ignoring cos x = 3/2 as −1 ≤ cos x ≤ 1. So, we have, sin 2x = cos 2x.
=> tan 2x = 1
=> tan 2x = tan π/4
=> 2x = nπ + π/4
=> x = nπ/2 + π/8, n ∈ Z