Question

If a+b+c = 15 and a^2+b^2+c^2 = 65 then find the value of ab+bc+ca

Answer 1

Answer:

80 = ab + bc + ca

Step-by-step explanation:

a + b + c = 15

a² + b² + c² = 65

(a + b + c)² = 15² = 225

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

225 = 65 + 2 (ab + bc + ca)

225 - 65 = 2 (ab + bc + ca)

160 = 2 (ab + bc + ca)

160 / 2 = ab + bc + ca

80 = ab + bc + ca