Question

If x-y = 7 and xy = 9, find x² + y².

Answer 1

Answer:

x-y = 7

(x-y)^2 = 7^2

So,

x^2 + y^2 - 2xy = 49

So,

x^2 + y^2 = 49+2(7) = 63

So,

x^2 + y^2 = 63 !

Answer 2

(x-y)^2 = x² + y². - 2xy

put the the given value.

(7)^2 = x² + y².- 2(9)

49= x² + y².-18

x² + y² = 67.