Answer:
(x, y) = (-6, 0)
Step-by-step explanation:
The y-coefficients have opposite signs, so we can eliminate y-terms by multiplying both equations by a positive number and adding the results.
9 times the first equation plus 4 times the second gives ...
9(5x +4y) +4(3x -9y) = 9(-30) +4(-18)
45x +36y +12x -36y = -270 -72 . . . . eliminate parentheses
57x = -342 . . . . . collect terms
x = -6 . . . . . . . divide by the coefficient of x
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Substituting into the first equation gives ...
5(-6) +4y = -30
4y = 0 . . . . . . . . . add 30
y = 0
The solution is (x, y) = (-6, 0).
