Question

if x+y = 9 and xy = 16 find the value of (x square + ysquare)

Answer 1

(x+y)²=x²+y²+ 2xy
x²+y²=(x+y)²-2xy
therefore,x²+y²=(9)²-2*16
=81-32
x²+y²=49

Answer 2

$(x+y)=9\\(x+y)^{2} =81\\x^{2} +2xy+y^{2} =81\\x^{2} +2(16)+y^{2} =81\\x^{2} +y^{2} =81-32\\x^{2} +y^{2} =49$