If x + y = 7/10 and x - y= 5/14, then x^2-y^2 =

a. (7/10)^2 - (5/14)^2
b. (1/2)^2
c. ( 5/14)^2
d. (7/10-5/14)^2

1 answer

well, x^2 - y^2 is the difference of squares, and
x^2 - y^2 = (x+y)(x-y)
= (7/10)(5/14) = 35/140 = 1/4

which of the given answers comes out to 1/4 ?