Question

If x+y+z=1,xy+yz+zx=-1 find the value of x2 +y2 +z2.

(A)3 (B)1 (C)2 (D)0

Answer 1

3 is the right answer using the identity

Answer 2

x+y+z=1
then we have (x+y+z)²=1²
                   ⇒ x²+y²+c²+2(xy+xz+zy)=1
substituting value of xy+yz+zx
⇒ x²+y²+z²-2=1
⇒ x²+y²+z²=²1+2=3