How do you solve the system $7 x - 8 y = 112$ $7x - 8y = 112$ and $y = - 2 x + 9$ $y = -2x +9$ by substitution?

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How do you solve the system $7 x - 8 y = 112$ $7x - 8y = 112$ and $y = - 2 x + 9$ $y = -2x +9$ by substitution?

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Answer 1 · 2015-05-28T19:07:08

You substitute the $y$ $y$ -value of the second equation into the first:

$\to 7 x - 8 \cdot (- 2 x + 9) = 112$ $->7x-8*(-2x+9)=112$
$\to 7 x + 16 x - 72 = 112$ $->7x+16x-72=112$
$\to 23 x = 184 \to x = \frac{184}{23} = 8$ $->23x=184->x=184/23=8$

Now put back the value of $x$ $x$ in the second equation:
$y = - 2 \cdot 8 + 9 = - 7$ $y=-2*8+9=-7$

So $x = 8 and y = - 7$ $x=8 and y=-7$

Check your answer with the first equation:
$7 \cdot 8 - 8 \cdot (- 7) = 56 - (- 56) = 112$ $7*8-8*(-7)=56-(-56)=112$ check!

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How do you solve the system $7 x - 8 y = 112$ $7x - 8y = 112$ and $y = - 2 x + 9$ $y = -2x +9$ by substitution?

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How do you solve the system 7x - 8y = 1127x−8y=1127x - 8y = 112 and y = -2x +9y=−2x+9y = -2x +9 by substitution?

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How do you solve the system $7 x - 8 y = 112$ $7x - 8y = 112$ and $y = - 2 x + 9$ $y = -2x +9$ by substitution?