algebra

Hey, I don't undertand how to solve this equation using substitution.

3y = -1/2x + 2
y= x + 9

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1. sub the 2nd into the 1st

3y = (1/2)x + 2
3(x+9) = (-1/2)x + 2
3x + 27 = (-1/2)x + 2
times 2 to get rid of that nasty fraction

6x + 54 = -x + 4
7x = -50
x = -50/7

then y = x+9 = -50/7 + 9 = 13/7

check:
in #1:
3y = (-1/2)x + 2
LS = 3(13/7) = 39/7
RS =(-1/2)(-50/7) + 14/7
= 25/7 + 14/7 = 39/7 = LS

my answer is correct.

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posted by Reiny

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