a + b + c = 15 এবং  a + b + c = 83 হলে ab + bc + ca = কত ?  

A 50 

B 61 

C 71 

D 99 

Solution

Correct Answer: Option C

a+b+c = 15 , a+b+c = 83, 

We know that, 

2(ab+bc+ca ) = (a+b+c ) - (a+b+c

or, ab+bc+ca = \(\frac{{(a + b + c)2 - (a2 + b2 + c2)}}{2} = \frac{{15 - 83}}{2} = \frac{{225 - 83}}{2}\)  = 71 

Practice More Questions on Our App!

Download our app for free and access thousands of MCQ questions with detailed solutions