Correct Answer - Option 4 : 50
Given
a + b + c = 13; a2 + b2 + c2 = 69.
Formula used
(a + b + c)2 = a2 + b2 + c2 + 2(ab + bc + ca)
Calculation
(a + b + c)2 = 132 = 169
⇒ 169 = 69 + 2(ab + bc + ca)
⇒ (ab + bc + ca) = (169 - 69)/2
⇒ (ab + bc + ca) = 50
∴ The value of (ab + bc + ca) is 50