Question

If a+b+c=0 and a²+b²+c²
Find value of
ab +bc+ca​

Answer 1

Formula :

(a +b+c) ^2 = a^2+b^2+c^2 + 2ab+2bc+2ac

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putting the values of a+b+c and a^2+b^2+c^2 in the given formula to get

0 = 16 + 2 (ab+bc+ac)

-16 = 2(ab+bc+ac)

-16/2 = ab+bc+ac

-8 = ab+bc+ac

Hence, the value of ab+bc+ac = -8

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(Note : The value of a^2+b^2+c^2 =16, as told by the questioner)