Question

if x+y+z=8 and xy +yz+zx=13 then find the value of x^2 +y^2 +z^2

Answer 1

(x+y+z)^2= x2+y2+z2+ 2(xy+yz+zx)
so by this formula we do
8^2 = ?+ 2(13)
?= 64-26
the answer is 38