a + b + c = 9, a2 + b2 + c2 = 29 হলে ab + bc + ca = কত?

a + b + c = 9, a² + b² + c² = 29 হলে ab + bc + ca = কত?

A 28

B 20

C 25

D 26

Correct Answer: Option D

a²+b²+c²=(a+b+c)²-2(ab+bc+ca)
=> 29 =(9)²-2(ab+bc+ca)
=> 2(ab+bc+ca) =81-29

∴ab+bc+ca=26