Question

If 9x+2y2−3z2=132 and 9y−2y2+3z2=867, then x+y =

Answer 1

Looking at these two equations, you need to cancel out the variables with powers and the z. This can be simply done by adding them.

9y-2y^2+3z^2=867
+
9x+2y^2-3z^2=132
-----------------------------
9y+9x=999

Factor the 9 out of the left side.
9(x+y)=999
x+y=111

The answer is C (111).