Question 1116288
 how do I solve -x-5y+z=17
                -x-y+z=1
                2x+5y-3z=-10  
<pre>- x - 5y + z = 17 ------- eq (i)
- x - y + z = 1 --------- eq (ii)
2x + 5y - 3z = - 10 ----- eq (iii)
4y = - 16  -------- Subtracting eq (i) from eq (ii)
Right away you can see that {{{highlight_green(matrix(1,5, y, "=", (- 16)/4, "=", - 4))}}}
- x - 5(- 4) + z = 17 ------- Substituting - 4 for y in eq (i)
- x + 20 + z = 17
- x + z = - 3 ------- eq (iv)

2x + 5(- 4) - 3z = - 10 ------- Substituting - 4 for y in eq (iii)
2x - 20 - 3z = - 10
2x - 3z = 10 ------- eq (v)
- 3x + 3z = - 9 ------- Multiplying eq (iv) by 3 ------ eq (vi)
- x = 1 ------- Adding eqs (v) & (vi)
{{{highlight_green(matrix(1,5, x, "=", 1/(- 1), "=", - 1))}}}
I leave it to you to find z
By the way. z CAN NEVER = 28, as YOU-KNOW-WHO will have you believe!