Question

If a^2 + b^2 + c^2 = 41 and a + b + c = 9, then find ab + bc + ca.

FORMULA =
(a + b + c)^2 = a^2 + b^2 + c^2 + 2ab + 2bc + 2ca

Answer 1

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Answer 2

• Solution:

a² + b² + c²= 41 ,a+b+c= 9

41 = a² + b² + c² + 2ab + 2bc +2ca

41 = (a² + b² + c²) + 2ab + 2bc +2ca

41 = (9²) + 2ab + 2bc +2ca

41 = 81 + 2ab + 2bc +2ca

41 - 81 = 2ab + 2bc +2ca

-40 = 2( ab + bc + ca)

20 = ab + bc + ca,,