Question

Solve:
$3x+4y+5z=18,2x-y+8z=13,5x-2y+7z=20$

Answer 1

$3x+4y+5z=18----\left(1\right)$

$2x-y+8z=13----\left(2\right)$

$5x-2y+7z=20---\left(3\right)$

multiply by $\left(4\right)$ in $\left(2\right)$ equation

$\frac{3x+4y+5z=188x-4y+32z=52}{11x+37z=70}---\left(4\right)$

multiply by $\left(2\right)$ in $\left(2\right)$ equation

$\frac{4x-2y+16z=265x-2y+7z=40}{-4---4+9z=-14-9x+99z=-1411x+37z=70\_\_\_\_\_\_\_\_\_\_\_\_136z=84}$

$34z=\frac{-21}{34}$

$11x+37\frac{-21}{34}=70$

$11x=70+\frac{777}{34}$

$11x=\frac{3157}{34}$

$x=\frac{3157}{374}$