Question

if x+y+z=12 and x^2+y^2+z^2=64 then find the value of xy+yz+zx

Answer 1

Please see the attachment

Answer 2

x+y+z=12
squaring both sides
(x+y+z)²=144
x²+y²+z²+2xy+2yz+2zx=144
64+2(xy+yz+zx)=144
2(xy+yz+zx)=144-64
xy+yz+zx=80/2
xy+yz+zx=40...