Solve the equation.
$\begin{pmatrix} 2 & 1 & 5 \\ 3 & -2 & 1 \\ 7 & -11 & 3 \end{pmatrix}\begin{pmatrix} x \\ y \\ z \end{pmatrix} = \begin{pmatrix} 4 \\ -17 \\ 20 \end{pmatrix}$
+128406 2x + y + 5z = 4
3x - 2y + z = -17
7x - 11y + 3z = 20
Multiply the first equation by 2 = 4x + 2y + 10z = 8
Add this to the second equation = 7x + 11z = -9 ( a)
Multiply the first eqation by 11 = 22x + 11y + 55z = 44
Add this to the third equation 29x + 58z = 64 (b)
Multiply (a) by 29 = 203 x + 319z = -261
Multiply (b) by - 7 = -203x - 406z = -448
Add the last two equations
-87z = -709
z = 709 / 87
7x + 11(709/87) = -9
7x = -9 - 11 ( 709/87) =
7x = -8582/87
x = -8582 /( 87 * 7)= -1226/87
And
2 (-1226 / 87) + y = 5( 709 / 87) = 4
y = 4 + 2(1226)/87 - 5 (709) / 87
y = -745 / 87
