Question

Решите матричные уравнения:

Answer 1

$A=\left(\begin{array}{cc}-8&-2\\5&1\end{array}\right)\ \ \ ,\ \ \ B=\left(\begin{array}{cc}5&-1\\1&1\end{array}\right)\\\\\\a)\ \ AX=B\ \ \ \Rightarrow \ \ \ X=A^{-1}\cdot B\\\\\\detA=-8+10=2$

$A_{11}=1\ \ ,\ \ A_{12}=-5\\A_{21}=2\ \ ,\ \ A_{22}=-8\ \ \ \qquad \qquad \ \ A^{-1}=\dfrac{1}{2}\cdot \left(\begin{array}{cc}1&2\\-5&-8\end{array}\right)\\\\\\X=\dfrac{1}{2}\cdot \left(\begin{array}{cc}1&2\\-5&-8\end{array}\right)\cdot \left(\begin{array}{cc}5&-1\\1&1\end{array}\right)=\dfrac{1}{2}\cdot \left(\begin{array}{cc}7&1\\-33&-3\end{array}\right)= \left(\begin{array}{cc}3,5&0,5\\-16,5&-1,5\end{array}\right)$

$b)\ \ \ XA=B\ \ \ \Rightarrow \ \ \ X=B\cdot A^{-1}$

$A^{-1}=\dfrac{1}{2}\cdot \left(\begin{array}{cc}1&2\\-5&-8\end{array}\right)\\\\\\X=\dfrac{1}{2}\cdot \left(\begin{array}{cc}5&-1\\1&1\end{array}\right)\cdot \left(\begin{array}{cc}1&2\\-5&-8\end{array}\right)=\dfrac{1}{2}\cdot \left(\begin{array}{cc}10&18\\-4&-6\end{array}\right)=\left(\begin{array}{cc}5&9\\-2&-3\end{array}\right)$