Question

If x² + y² + z² = 20 and x + y + z = 0, then xy + yz + zx is equal to :

(A) 10 (B) –10 (C) 8 (D) –8

Answer 1

hey mate here's ur ans ↑↑

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hope it helps u☺☺✌

Answer 2

here firstly x + y +. z = 0
by sq. both sides
(x+y+z) ^2 = 0^2
x^2 + y^2 + z ^2 +2xy +2yz +2zx =0
20 +2(xy +yz +zx) = 0
soo
xy +yz +zx =-20 /2 = -10
hence (b )option is right....

HOPE IT HELPS YOU!!!!!