a+b+c=35 এবং a2+b2+c2=825 হলে ab+bc+ca=?

a+b+c=35 এবং a2+b2+c2=825 হলে ab+bc+ca=?

A 100

B 200

C 125

D 225

Solution

Correct Answer: Option B

2(ab+bc+ca)=(a+b+c)²-(a²+b²+c²)
or,ab+bc+ca=(35²-825)/2=400/2
অতএব,ab+bc+ca=200