solve by elimination

Question

2x - y - z =15

4x + 5y + 2z = 10

-x - 4y + 3z = -20

Answer 1

Eliminates z:

row2 = 2*row1+row2

row3 = 3*row1+row3

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8x + 3y = 40

5x - 7y = 25

row1 = 7 * row1

row2 = 3 * row2

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56x + 21y = 280

15x - 21y = 75

71x = 315

x = 5

Next in the 2x2:

8(5) +3y = 50

5(5) - 7y = 25

40 + 3y = 40

25 - 7y = 25

3y = 0 and -7y = 0

y = 0

then from the original first equation:

2(5) - 0 - z = 15

10 - z = 15

-z = 5

z = -5

the solution set is x=5, y=0, z = -5

the check is left for you, but it does check!