Let A = $\left[ {\matrix{
x & 1 \cr
1 & 0 \cr
} } \right]$, x $\in$ R and A4 = [aij].
If
a11 = 109, then a22 is equal to _______ .
Answer (integer)
10
Solution
$${A^2} = \left[ {\matrix{
x & 1 \cr
1 & 0 \cr
} } \right]\left[ {\matrix{
x & 1 \cr
1 & 0 \cr
} } \right] = \left[ {\matrix{
{{x^2} + 1} & x \cr
x & 1 \cr
} } \right]$$<br><br>$${A^4} = \left[ {\matrix{
{{x^2} + 1} & x \cr
x & 1 \cr
} } \right]\left[ {\matrix{
{{x^2} + 1} & x \cr
x & 1 \cr
} } \right]$$<br><br>$$ = \left[ {\matrix{
{{{({x^2} + 1)}^2} + {x^2}} & {x({x^2} + 1) + x} \cr
{x({x^2} + 1) + x} & {{x^2} + 1} \cr
} } \right]$$<br><br>Given ${({x^2} + 1)^2} + {x^2} = 109$<br><br>Let ${x^2} + 1$ = t<br><br>${t^2} + t - 1 = 109$<br><br>$\Rightarrow$ (t $-$ 10) (t + 11) = 0<br><br>$\therefore$ t = 10 = x<sup>2</sup> + 1 = a<sub>22</sub>
About this question
Subject: Mathematics · Chapter: Matrices and Determinants · Topic: Types of Matrices and Operations
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