Question

x - y + z = 5

3x + 2y - z = -2

2x + y + 3z = 10

(elimination or substitution is acceptable)

Answer 1

1.add the first two eq.
2.multiply second by 3 then add in third

Answer 2

x - y + z = 5
3x + 2y - z = -2
--------------add
4x + y = 3

3x + 2y - z = -2 -->(3)
2x + y + 3z = 10
---------------
9x + 6y - 3z = -6 (result of multiplying by 3)
2x + y + 3z = 10
----------------add
11x + 7y = 4

4x + y = 3 --->(-7)
11x + 7y = 4
-----------------
-28x - 7y = -21(result of multiplying by -7)
11x + 7y = 4
-----------------add
-17x = - 17
x = 1

4x + y = 3
4(1) + y = 3
4 + y = 3
y = 3 - 4
y = -1

x - y + z = 5
1 - (-1) + z = 5
1 + 1 + z = 5
z = 5 - 2
z = 3

check...
3x + 2y - z = -2
3(1) + 2(-1) - 3 = -2
3 - 2 - 3 = -2
-2 = -2 (correct)

x = 1, y = -1, z = 3

Answer 3

Didn't they already help you?

Answer 4

yes but i noticed a part later that i didnt understand

Answer 5

i dont understand where that -7 came from...

Answer 6

I'm not good with this level of math, but maybe someone else can help you.

Answer 7

okay, thank you anyway :)

Answer 8

i dont see where that -7 came from...

Answer 9

the idea is to make the coefficient of y or x the same.
if they are of opposite sign ,then we add.
if they are of same sign,then we subtract.