Question

−3x + 7y = −16
−9x + 5y = 16

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Answer 1

{-3x+7y=-16 ⇒ -3x=-16-7y (↓)

{-9x+5y=16

The second equation:

-9x+5y=16

3*(-3x)+5y=16 Substitute -3x (↑)

3* (-16-7y)+5y=16

-48-21y+5y=16 /+48

-16y=64 /:(-16)

y=-4

-3x=-16-7y

-3x=-16-7*(-4)=-16+28=12

-3x=12 /:(-3)

x=-4

Solution: (-4; -4)