SOLUTION: solve by using subsitution 4x+4y=-20 x-4y=15

Question 698784: solve by using subsitution
4x+4y=-20
x-4y=15

Answer by Simnepi(216) (Show Source): You can put this solution on YOUR website!
4x+4y=-20 Equation (1)
x-4y=15 Equation (2)
Rearranging (2) gives
x=15+4y Equation (3)
We can now substitute the value of x from (3) into (1)
4*(15+4y)+4y = -20
Multiplying out and simplifying we get
60+20y = -20
therefore 20y = -80
which gives y = -4
Now we can substitute this value of y into either (1), (2) or (3) to find the value of x
lets use (3)
x=15+4y
x=15+4*-4
so x= -1
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