Andrew M. answered • 05/14/15
Tutor
New to Wyzant
Mathematics - Algebra a Specialty / F.I.T. Grad - B.S. w/Honors
2X + 3Y = -8
X - 4Y = 7
In order to eliminate one variable we need to get rid of one of the variables...
We do this by changing one equation so that one variable has the same number with opposite sign as in the other equation. If we multiply the 2nd equation through by -2 we will have 2X in the 1st equation and -2X in the 2nd so that they will be eliminated when we add the two equations.
2X + 3Y = -8
-2(X - 4Y = 7)
2X + 3Y = -8
-2X + 8Y = -14
Adding straight down we get 11Y = -22
Divide out the 11 giving Y = -2
We can now use the known value of Y = -2 in either of the original equations to find X
X - 4Y = 7
X -4(-2) = 7
X + 8 = 7
X = -1
So our two variables are X = -1, Y = -2
