If (x+y)^2=168 and xy =4, then x^2 + y^2=?

Answer 1

(x+y)^2 = 168
x^2 + 2xy + y^2 = 168
Replace xy with 4:
x^2 + 2*4 + y^2 = 168
x^2 + y^2 = 168 - 8 = 160.