Question

if x+y=8 and xy=15,findx2+y2

Answer 1

We have:

(x+y)^2= x^2+y^2+2xy

(8)^2= x^2+y^2+2×15

64= x^2+y^2+30

64-30=x^2+y^2

Therefore,

x^2+y^2=34