solve by elimination

Question

2x -y - z =15

4x + 5y + 2z = 10

-x - 4y + 3z = -20

Answer 1

2x -y - z =15

z+15=2x-y

z=2x-y-15

4x + 5y + 2z = 10

4x+5y+2(2x-y-15)=10

4x+5y+4x-2y-30=10

8x+3y-30=10

8x+3y=40

3y=40-8x

y=40/3-8/3x

z=2x-y-15

z=2x-40/3+8/3x-15

z=6/3x+8/3x-40/3-45/3

z=14/3x-85/3

-x - 4y + 3z = -20

-x-4(40/3-8/3x)+3(14/3x-85/3)=-20

-x-160/3+32/3x+14x-85=-20

-3x-160+32x+42x-255=-60

71x-415=-60

71x=355

x=5

y=40/3-8/3(5)

y=-40/3-40/3

y=0

z=14/3(5)-85/3

z=70/3-85/3

z=-15/3

z=-5