SarkariPYQ

SSC CGL 2019 PYQ — Question 58

SSC CGL - 4th June 2019 - Shift 3 • Quantitative Aptitude • Q58

Back to paper

If a2 + b2 + c2 = 21 and a + b + c = 7, then (ab + bc + ca) is equal to:

Show answer & explanation

Correct answer: A

Explanation

Correct Answer is option 1 i.e. 14

Understanding

Application

Given:

a2 + b2 + c2 = 21

and

a + b + c = 7

Using formula:

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

⇒ 49 = 21 + 2(ab + bc + ca)

⇒ (49 – 21)/2 = (ab + bc + ca)

⇒ (ab + bc + ca) = 14