Question

Find ab+bctca

If a2 + b2 + c2 = 30 and a + b + c = 0​

Answer 1

GIVEN:

a2 + b2 + c2 = 30 and a + b + c = 0

TO FIND:

ab+bc+ca = ?

SOLUTION:

We already know the formula:

(a + b + c)2 = a2 + b2 + c2 + 2(ab + bc + ca)

substitute the known values in the above formula

∴ (0)2 = 30 + 2(ab + bc + ca)

∴ 2(ab + bc + ca) = 0-30

ab + bc + ca = -30/2

⇒ ab + bc + ca = -15

Feel free to ask if you have any doubt in the process..