Question

is a2 + b2 + c2 = 20 and a +b+c= 10, ab + bc + ca is equal to
80
20
40
160​

Answer 1

Answer: 155

Step-by-step explanation:

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

(20)²= +90 + 2(ab+ bc+ ca)

400=90 + 2(ab+ bc+ ca)

400 - 90 =2(ab+ bc+ ca)

310 = 2(ab+ bc+ ca)

(ab + bc + ca) = 310/2

∴(ab + bc + ca) = 155