证明以下三角恒等式:
问题1.(1-cos 2 A)cosec 2 A = 1
解决方案:
We have,
L.H.S. = (1 – cos2 A) cosec2 A
By using the identity, sin2 A + cos2 A = 1, we get,
= (sin2 A) (cosec2 A)
= sin2 A × (1/sin2 A)
= 1
= R.H.S.
Hence proved.
问题2.(1 +轻便小床2 A)罪2 A = 1
解决方案:
We have,
L.H.S. = (1 + cot2 A) sin2 A
By using the identity, cosec2 A = 1 + cot2 A, we get,
= cosec2 A sin2 A
= (1/sin2 A) × sin2 A
= 1
= R.H.S
Hence proved.
问题3黄褐色2个θCOS 2θ= 1 – COS 2θ
解决方案:
We have,
L.H.S. = tan2 θ cos2 θ
= (sin2 θ/cos2 θ) (cos2 θ)
= sin2 θ
= 1 − cos2 θ
= R.H.S.
Hence proved.
问题4. cosecθ√(1-cos 2θ )= 1
解决方案:
We have,
L.H.S. = cosec θ √(1 – cos2 θ)
= cosec θ √(sin2 θ)
= cosec θ sin θ
= (1/sin θ) (sin θ)
= 1
= R.H.S.
Hence proved.
问题5.(sec 2θ -1)(cosec 2θ -1)= 1
解决方案:
We have,
L.H.S. = (sec2 θ − 1)(cosec2 θ − 1)
By using the identities sec2 θ − tan2 θ = 1 and cosec2 θ − cot2 θ = 1, we have,
= tan2 θ cot2 θ
= (tan2 θ) (1/tan2 θ)
= 1
= R.H.S.
Hence proved.
问题6. tanθ+ 1 / tanθ= secθcosecθ
解决方案:
We have,
L.H.S. = tan θ + 1/ tan θ
= (tan2 θ + 1)/tan θ
= sec2 θ/tan θ
=
=
= 1/sin θ cos θ
= sec θ cosec θ
= R.H.S.
Hence proved.
问题7. cosθ/(1 – sinθ)=(1 + sinθ)/ cosθ
解决方案:
We have,
L.H.S. = cos θ/(1 – sin θ)
=
=
=
= (1 + sin θ)/cos θ
= R.H.S.
Hence proved.
问题8. cosθ/(1 + sinθ)=(1 – sinθ)/ cosθ
解决方案:
We have,
L.H.S. = cos θ/(1 + sin θ)
=
=
=
= (1 – sin θ)/cos θ
= R.H.S.
Hence proved.
问题9. cos 2θ + 1 /(1 + cot 2θ )= 1
解决方案:
We have,
L.H.S. = cos2 θ + 1/(1 + cot2 θ)
= cos2 θ + 1/(cosec2 θ)
= cos2 θ + sin2 θ
= 1
= R.H.S.
Hence proved.
问题10.sin 2 A +1 /((1 + tan 2 A)= 1
解决方案:
We have,
L.H.S. = sin2 A + 1/(1 + tan2 A)
= sin2 A + 1/(sec2 A)
= sin2 A + cos2 A
= 1
= R.H.S.
Hence proved.
问题11 = cosecθ-cotθ
解决方案:
We have,
L.H.S. =
=
=
=
=
=
= cosec θ − cot θ
= R.H.S.
Hence proved.
问题12.(1 – cosθ)/ sinθ= sinθ/(1 + cosθ)
解决方案:
We have,
L.H.S. = (1 – cos θ)/sin θ
=
=
=
= sin θ/(1 + cos θ)
= R.H.S.
Hence proved.
问题13.正弦θ/(1 – cosθ)= cosecθ+科特角θ
解决方案:
We have,
L.H.S. = sin θ/(1 – cos θ)
=
=
=
=
=
= cosec θ + cot θ
= R.H.S.
Hence proved.
问题14.(1 – sinθ)/(1 + sinθ)=(secθ– tanθ) 2
解决方案:
We have,
L.H.S. = (1 – sin θ)/(1 + sin θ)
=
=
=
=
=
= (sec θ – tan θ)2
= R.H.S.
Hence proved.
问题15。
解决方案:
We have,
L.H.S. =
=
=
= cos θ/sin θ
= cot θ
= R.H.S.
Hence proved.
问题16黄褐色2θ -罪2θ=黄褐色2θ罪2θ
解决方案:
We have,
L.H.S. = tan2 θ − sin2 θ
= sin2 θ/cos2 θ − sin2 θ
= sin2 θ(1/cos2 θ − 1)
=
= sin2θ (sin2θ/cos2θ)
= tan2 θ sin2 θ
= R.H.S.
Hence proved.
问题17。(cosecθ+ sinθ)(cosecθ– sinθ)= cot 2θ + cos 2θ
解决方案:
We have,
L.H.S. = (cosec θ + sin θ)(cosec θ – sin θ)
= cosec2 θ – sin2 θ
= (1 + cot2 θ) – (1 – cos2 θ)
= 1 + cot2 θ – 1 + cos2 θ
= cot2 θ + cos2 θ
= R.H.S.
Hence proved.
问题18。(秒θ+ cosθ)(秒θ– cosθ)= tan 2θ + sin 2θ
解决方案:
We have,
L.H.S. = (sec θ + cos θ) (sec θ – cos θ)
= sec2 θ – cos2 θ
= (1 + tan2 θ) – (1 – sin2 θ)
= 1 + tan2 θ – 1 + sin2 θ
= tan2 θ + sin2 θ
= R.H.S
Hence proved.
问题19.秒A(1-正弦A)(秒A +棕褐色A)= 1
解决方案:
We have,
L.H.S. = sec A(1 – sin A) (sec A + tan A)
=
=
=
= 1
= R.H.S
Hence proved.
问题20.(cosec A – sin A)(sec A – cos A)(tan A + cot A)= 1
解决方案:
We have,
L.H.S. = (cosec A – sin A)(sec A – cos A)(tan A + cot A)
=
=
=
= 1
= R.H.S
Hence proved.
问题21.(1 + tan 2θ )(1 – sinθ)(1 + sinθ)= 1
解决方案:
We have,
L.H.S. = (1 + tan2 θ)(1 – sin θ)(1 + sin θ)
= (sec2 θ) (1 – sin2 θ)
= (sec2 θ) (cos2 θ)
= 1
= R.H.S
Hence proved.
问题22.sin 2婴儿床2 A + cos 2 A棕褐色2 A = 1
解决方案:
We have,
L.H.S. = sin2 A cot2 A + cos2 A tan2 A
= sin2 A (cos2 A/sin2 A) + cos2 A (sin2 A/cos2 A)
= cos2 A + sin2 A
= 1
= R.H.S.
Hence proved.
问题23。
(i)婴儿床θ–棕褐色θ=
解决方案:
We have,
L.H.S. = cot θ – tan θ
= cos θ/sin θ – sin θ/cos θ
=
=
=
=
= R.H.S.
Hence proved.
(ii)tanθ– cotθ =
解决方案:
We have,
L.H.S. = tan θ – cot θ
= sin θ/cos θ – cos θ/sin θ
=
=
=
=
= R.H.S.
Hence proved.
问题24.(cos 2θ / sinθ)– cosecθ+ sinθ= 0
解决方案:
We have,
L.H.S. = (cos2 θ/sin θ) – cosec θ + sin θ
=
=
=
= 0
= R.H.S.
Hence proved.
问题25。
解决方案:
We have,
L.H.S. =
=
=
=
= 2 sec2 A
= R.H.S.
Hence proved.
问题26。
解决方案:
We have,
L.H.S. =
=
=
=
=
= 2 sec θ
= R.H.S.
Hence proved.
问题27。
解决方案:
We have,
L.H.S. =
=
=
=
= R.H.S.
Hence proved.
问题28。
解决方案:
We have,
L.H.S. =
= sec2 θ/cosec2 θ
=
= tan2 θ
= R.H.S.
Hence proved.