第 12 类 RD Sharma 解决方案 - 第 5 章矩阵代数 - 练习 5.3 |设置 2
问题 26. 如果 = 0,求 x。
解决方案:
We have,
=>= 0
=>
=>
=>
=> 2x – 4 = 0
=> 2x = 4
=> x = 2
Therefore, the value of x is 2.
问题 27. 如果 A = 我 = ,然后证明 A 2 – A + 2I = 0。
解决方案:
We have,
A =
A2 =
=
=
L.H.S. = A2 – A + 2I
=
=
=
=
=
=
= 0
= R.H.S.
Hence proved.
问题 28. 如果 A = 我 = ,然后找到λ使得 A 2 = 5A + λI。
解决方案:
We have,
A =
A2 =
=
=
We are given,
=> A2 = 5A + λI
=>
=>
=>
=>
On comparing both sides, we get
=> 8 = 15 + λ
=> λ = –7
Therefore, the value of λ is –7.
问题 29. 如果 A = ,证明 A 2 – 5A + 7I 2 = 0。
解决方案:
We have,
A =
A2 =
=
=
L.H.S. = A2 – 5A + 7I2
=
=
=
=
= 0
= R.H.S.
Hence proved.
问题 30. 如果 A = ,证明 A 2 – 2A + 3I 2 = 0。
解决方案:
We have,
A =
A2 =
=
=
L.H.S. = A2 – 2A + 3I2
=
=
=
=
= 0
= R.H.S.
Hence proved.
问题 31. 证明矩阵 A = 满足方程 A 3 – 4A 2 + A = 0。
解决方案:
We have,
A =
A2 =
=
=
A3 = A2. A
=
=
=
L.H.S. = A3 – 4A2 + A
=
=
=
=
= 0
= R.H.S.
Hence proved.
问题 32. 证明矩阵 A = 是方程 A 2 – 12A – I = 0 的根
解决方案:
We have,
A =
A2 =
=
=
L.H.S. = A2 – 12A – I
=
=
=
=
= 0
= R.H.S.
Hence proved.
问题 33. 如果 A = 找到 A 2 – 5A – 14I。
解决方案:
We have,
A =
A2 =
=
=
A2 – 5A – 14I =
=
=
=
问题 34. 如果 A = ,找到 A 2 – 5A + 7I = 0。用它来找到 A 4 。
解决方案:
We have,
A =
A2 =
=
=
L.H.S. = A2 – 5A + 7I = 0
=
=
=
=
= 0
= R.H.S.
Hence proved.
Now we have A2 – 5A + 7I = 0
=> A2 = 5A – 7I
=> A4 = (5A – 7I) (5A – 7I)
=> A4 = 25A2 – 35AI – 35AI + 49I
=> A4 = 25A2 – 70AI + 49I
=> A4 = 25 (5A – 7I) – 70AI + 49I
=> A4 = 125A – 175I – 70A + 49I
=> A4 = 55A – 126I
=> A4 =
=> A4 =
=> A4 =
=> A4 =
问题 35. 如果 A = ,求 k 使得 A 2 = kA – 2I 2 。
解决方案:
We have,
A =
A2 =
=
=
We are given,
=> A2 = kA – 2I2
=>
=>
=>
On comparing both sides, we get
=> 3k – 2 = 1
=> 3k = 3
=> k = 1
Therefore, the value of k is 1.
问题 36. 如果 A = ,求 k 使得 A 2 – 8A + kI = 0。
解决方案:
We have,
A =
A2 =
=
=
We are given,
=> A2 – 8A + kI = 0
=>
=>
=>
=>
On comparing both sides, we get
=> –k + 7 = 0
=> k = 7
Therefore, the value of k is 7.
问题 37. 如果 A = 和 f(x) = x 2 – 2x – 3,证明 f(A) = 0。
解决方案:
We have,
A =and f(x) = x2 – 2x – 3
A2 =
=
=
L.H.S. = f(A) = A2 – 2A – 3I2
=
=
=
=
= 0
= R.H.S.
Hence proved.
问题 38. 如果 A = 我 = , 求 λ, μ 使得 A 2 = λA + μI。
解决方案:
We have,
A =
A2 =
=
=
We are given,
=> A2 = λA + μI
=>
=>
=>
=>
On comparing both sides, we get,
=> 2λ + μ = 7 and λ = 4
=> 2(4) + μ = 7
=> μ = 7 – 8
=> μ = –1
Therefore, the value of λ is 4 and μ is –1.
问题 39. 求矩阵乘积的 x 值等于单位矩阵。
解决方案:
We have,
=>
=>
=>
On comparing both sides, we get,
=> 5x = 1
=> x = 1/5
Therefore, the value of x is 1/5.
问题 40. 求解下列矩阵方程:
(一世)
解决方案:
We have,
=>
=>
=>
=>
=> x2 – 2x – 15 = 0
=> x2 – 5x + 3x – 15 = 0
=> x (x – 5) + 3 (x – 5) = 0
=> (x – 5) (x + 3) = 0
=> x = 5 or –3
Therefore, the value of x is 5 or –3.
(二)
解决方案:
We have,
=>
=>
=>
=>
=> 4 + 4x = 0
=> 4x = –4
=> x = –1
Therefore, the value of x is –1.
㈢
解决方案:
We have,
=>
=>
=>
=>
=> x2 – 48 = 0
=> x2 = 48
=> x = ±4√3
Therefore, the value of x is ±4√3.
(四)
解决方案:
We have,
=>
=>
=>
=>
=> 2x2 + 23x = 0
=> x (2x + 23) = 0
=> x = 0 or x = –23/2
Therefore, the value of x is 0 or –23/2.
问题 41. 如果 A = ,计算 A 2 – 4A + 3I 3 。
解决方案:
We have,
A =
A2 =
=
=
So, A2 – 4A + 3I3 =
=
=
=
问题 42. 如果 f(x) = x 2 – 2x,求 f(A),其中 A = .
解决方案:
We have,
A =and f(x) = x2 – 2x
A2 =
=
=
So, f(A) = A2 – 2A
=
=
=
=
问题 43. 如果 f(x) = x 3 + 4x 2 – x,求 f(A) 其中 A = .
解决方案:
We have,
A =and f(x) = x3 + 4x2 – x
A2 =
=
=
A3 = A2. A
=
=
=
Now, f(A) = A3 + 4A2 – A
=
=
=
=
问题 44. 如果 A = ,然后证明 A 是多项式 f(x) = x 3 – 6x 2 + 7x +2 的根。
解决方案:
We have,
A =and f(x) = x3 – 6x2 + 7x +2.
A2 =
=
=
A3 = A2. A
=
=
=
In order to show that A is a root of above polynomial, we need to prove that f(A) = 0.
Now, f(A) = A3 – 6A2 + 7A + 2I
=
=
=
=
= 0
Hence proved.
问题 45. 如果 A = ,证明 A 2 – 4A – 5I = 0。
解决方案:
We have,
A =
A2 =
=
=
Now, L.H.S. = A2 – 4A – 5I
=
=
=
=
= 0
= R.H.S.
Hence proved.
问题 46. 如果 A = ,证明 A 2 – 7A + 10I 3 = 0。
解决方案:
We have,
A =
A2 =
=
=
Now, L.H.S. = A2 – 7A + 10I3
=
=
=
=
= 0
= R.H.S.
Hence proved.
问题 47. 不使用矩阵逆的概念,求矩阵这样,
解决方案:
We have,
=>
=>
On comparing both sides, we get,
5x – 7z = –16
5y – 7u = –6
–2x + 3z = 7
–2y + 3u = 2
On solving the above equations, we get
=> x = 1, y = –4, z = 3 and u = –2.
So, we get.
问题 48. 找到矩阵 A 使得
(一世)
解决方案:
Let A =
Given equation is,
=>
=>
=>
=>
On comparing both sides, we get, a = 1, b = 0 and c = 1.
And x + 1 = 3 => x = 2
Also, y = 3 and
z + 1 = 5 => z = 4
So, we have A =
(二)
解决方案:
Let A =
Given equation is,
=>
=>
=>
On comparing both sides, we get,
w + 4x = 7
2w + 5x = –6
y + 4z = 2
2y + 5z = 4
On solving the above equations, we get
=> x = –2, y = 2, w = 1 and z = 0.
So, we get A =
㈢
解决方案:
Let A =
Given equation is,
=>
=>
=>
On comparing both sides, we get,
=> 4x = – 4, 4y = 8 and 4z = 4.
=> x = –1, y = 2 and z = 1.
So, we get A =
(四)
解决方案:
We have,
A =
A =
A =
A =
(五)
解决方案:
Let A =
Given equation is,
=>
=>
=>
On comparing both sides, we get,
=> x = 1, y = –2 and z = –5
And also we have,
2x – a = –1
2y – b = –8
2z – c = –10
On solving these, we get,
=> a = 3, b = 4 and c = 0.
So, we get A =
(六)
解决方案:
Let A =
Given equation is,
=>
=>
=>
On comparing both sides, we get
x + 4a = –7 and 2x + 5a = –8
=> x = 1 and a = –2
y + 4b = 2 and 2y + 5b = 4
=> b = 0 and y = 2
z + 4c = 11 and 2z + 5c = 10
=> c = 4 and z = –5
So, we get A =
问题 49. 找到一个 2 × 2 矩阵 A 使得 = 6I 2 。
解决方案:
Let A =
Given equation is,
=>= 6I
=>
=>
=>
On comparing both sides, we get
w + x = 6 and –2w + 4x = 0
=> w = 4 and x = 2
y + z = 0 and –2y + 4z = 6
=> y = –1 and z = 1
So, we get A =
问题 50. 如果 A = ,找到 A 16 。
解决方案:
We have,
A =
A2 =
=
=
A16 = A2 A2 A2 A2
=
=
问题 51. 如果 A = , B = 和 x 2 = –1,然后证明 (A + B) 2 = A 2 + B 2 。
解决方案:
We have,
A =, B =and x2 = –1
L.H.S. = (A + B)2
=
=
=
=
=
=
=
=
R.H.S. = A2 + B2
=
=
=
=
=
=
= L.H.S.
Hence proved.