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If A=[0-tan α2tan α20] and I is the identity matrix of order 2, show that I + A = (I-A)[cosα-sinαsinαcosα] - Mathematics

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प्रश्न

if `A = [(0, -tan  alpha/2), (tan  alpha/2, 0)]` and I is the identity matrix of order 2, show that I + A = `(I -A)[(cos alpha, -sin alpha),(sin alpha, cos alpha)]`

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उत्तर

`A = [(0, -tan  alpha/2), (tan  alpha/2, 0)], I = [(1,0),(0,1)]` 

`I + A = [(1,0),(0,1)] + [(0, -tan  alpha/2), (tan  alpha/2, 0)]`

`= [(1, -tan  alpha/2), (tan  alpha/2, 1)]`

`(I - A) [(cos alpha, -sin alpha),(sin alpha, cos alpha)] = ([(1,0),(0,1)] - [(0, -tan alpha/2), (tan alpha/2, 0)]) [(cos alpha, -sin alpha),(sin alpha, cos alpha)]`

`= [(1, tan  alpha/2), (-tan  alpha/2, 1)] [(cos alpha, -sin alpha),(sin alpha, cos alpha)]` 

`= [(1, tan  alpha/2), (-tan  alpha/2, 1)]` `[((1 - tan^2  alpha/2)/(1 + tan^2  alpha/2)(-2  tan  alpha/2)/(1+ tan^2  alpha/2)),((-2 tan  alpha/2)/(1+ tan^2  alpha/2)(1 - tan^2  alpha/2)/(1 + tan^2  alpha/2))]`

`= [((1 + tan^2  alpha/2)/(1 + tan^2  alpha/2)(-tan  alpha/2 - tan^3  alpha/2)/(1+ tan^2  alpha/2)),((tan  alpha/2 + tan^3  alpha/2)/(1+ tan^2  alpha/2)(1 + tan^2  alpha/2)/(1 + tan^2    alpha/2))]`

`= [(1, -tan alpha/2),(tan alpha/2, 1)]`

Hence, `I + A = (I - A) [(cos alpha, -sin alpha),(sin alpha, cos alpha)]`

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अध्याय 3: Matrices - Exercise 3.2 [पृष्ठ ८२]

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एनसीईआरटी Mathematics Part 1 and 2 [English] Class 12
अध्याय 3 Matrices
Exercise 3.2 | Q 18 | पृष्ठ ८२

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