행렬 \( A=\left(\begin{array}{cc}2 & 1 \\ -1 & 3\end{array}\right) \) 에 대하여 \( \left(A^{-1}\right)^{2} \) 을 구하여라.

(2) \( 3 \sqrt{8}-\sqrt{\frac{1}{2}}= \)

olve the linear system \( \begin{array}{l}3 x_{1}-x_{2}+x_{3}+2 x_{4}=-2 \\ \qquad x_{1}+2 x_{2}-x_{3}+x_{4}=1 \\ -x_{1}-3 x_{2}-2 x_{3}-4 x_{4}=-6\end{array} \)

3. ( 3,1 ball) Bittadan ko'p sondagi mushuklar jami 221 ta sichqon yeyishdi. Agar har bir mushukning yegan sichqonlari soni teng va umumiy mushuklar sonidan ko'pligi ma'lum bo'lsa, mushuklar sonini aniqlang? \( \begin{array}{llll}\text { A) } 9 & \text { B) } 13 & \text { C) } 17 & \text { d) } 21\end{array} \)

(1) \( \sqrt{5}-\sqrt{\frac{4}{5}}= \)

5. If \( a=\sqrt{2}+1 \& b=\sqrt{2}-1 \), then \( \frac{1}{a+1}+\frac{1}{b+1}= \) ? \( \begin{array}{llll}\text { (a) } 9 & \text { (b) } 3 & \text { (c) } 1 & \text { (d) } 2\end{array} \)