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Exercise 7.5 · Q14

Q.If the square of the matrix [αβγ−α]\begin{bmatrix} \alpha & \beta \\ \gamma & -\alpha \end{bmatrix} is the unit matrix of order 22, then α,β\alpha, \beta and γ\gamma should satisfy the relation.

(1) 1+α2+βγ=01 + \alpha^2 + \beta\gamma = 0
(2) 1−α2−βγ=01 - \alpha^2 - \beta\gamma = 0
(3) 1−α2+βγ=01 - \alpha^2 + \beta\gamma = 0
(4) 1+α2−βγ=01 + \alpha^2 - \beta\gamma = 0
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Compute the square of the 2×22\times2 matrix and match II.

This tests matrix squaring and the identity condition.

Step 1. With M=[αβγ−α]M = \begin{bmatrix} \alpha & \beta \\ \gamma & -\alpha \end{bmatrix}, top-left of M2=α2+βγM^2 = \alpha^2 + \beta\gamma; top-right =αβ−βα=0= \alpha\beta - \beta\alpha = 0. …

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