Question 811434: Use addition to solve.
2x + 3y = -5
3x - 2y = 12
I know the answer is (7,0), but how to do I come to that answer?
Answer by Edwin McCravy(20056) (Show Source):
You can put this solution on YOUR website!
2x + 3y = -5
3x - 2y = 12
The answer is not (7,0). You must have looked at the
answer to the wrong problem.
We look at the two coefficients of y. They are +3 in the first
equation and -2 in the second. The least common multiple of |+3|
and |-2| is 6.
So if we multiply both sides of the first equation by 2 and
both sides of the second equation by 3, we get
4x + 6y = -10
9x - 6y = 36
Now when we add equals to equals, the +6y in the first will cancel
with the -6y in the second:
4x + 6y = -10
9x - 6y = 36
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13x = 26
x = 2
Then we substitute that in either or the original equations:
2x + 3y = -5
2(2) + 3y = -5
4 + 3y = -5
3y = -9
y = -3
So the answer is (2,-3).
Checking the first equation:
2x + 3y = -5
2(2) + 3(-3) = -5
4 - 9 = -5
-5 = -5
Checking the second equation:
3x - 2y = 12
3(2) - 2(-3) = 12
6 + 6 = 12
12 = 12
So the answer is (2,-3), not (7,0).
Edwin
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