1.

If a + b + c = 0 and a2 + b2 + c2 = 16, find the value of ab + bc + ca.

Answer»

Given,

a + b + c = 0 and a2 + b2 + c2 = 16

Choose a + b + c = 0 

Squaring both sides,

(a + b + c)2 = 0 

a2 + b2 + c2 + 2(ab + bc + ca) 

= 0 

16 + 2(ab + bc + c) = 0 

2(ab + bc + ca) = -16 

ab + bc + ca = \(\frac{-16}{2}\)

ab + bc + ca = -8



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