Question

If x+y =10 and x-y=11, what is the value of x^2-y^2?

Answer 1

110

Answer 2

the best thing to do is to line up both equation and for this question we add
so x+y=10
x-y=11
(x-x)+(y- -y)=(10-11)
0+2y= -1 NB: when you have two minus sign side by side you add
so when 2y= -1 y=-0.5
now that we have one unknown you just put 0.5 were y is in the first equation
x+0.5=10 so x=9.5
so 9.5^2-0.5^2 = 90.25-0.25= 90