Question

Use Cramer's Rule to solve the following system: –2x – 6y = –26 5x + 2y = 13

Answer 1

$\bf \begin{cases} -2x-6y&=-26\\ \quad 5x+2y&=13 \end{cases}\stackrel{\textit{determinant of the coefficients}}{D= \begin{bmatrix} -2&-6\\5&2 \end{bmatrix}}\implies (-4)-(-30) \\\\\\ D=-4+30\implies \boxed{D=26}\\\\ -------------------------------$

$\bf x=\cfrac{D_x}{D}\implies x=\cfrac{ \begin{bmatrix} \boxed{-26}&-6\\\\ \boxed{13}&2 \end{bmatrix}}{D}\implies x=\cfrac{(-52)-(-78)}{26} \\\\\\ x=\cfrac{-52+78}{26}\implies x=\cfrac{26}{26}\implies \boxed{x=1}\\\\ -------------------------------\\\\ y=\cfrac{D_y}{D}\implies y=\cfrac{ \begin{bmatrix} -2&\boxed{-26}\\\\ 5&\boxed{13} \end{bmatrix}}{D}\implies y=\cfrac{(-26)-(-130)}{26} \\\\\\ y=\cfrac{-26+130}{26}\implies y=\cfrac{104}{26}\implies \boxed{y=4}$