SSC CHSL 19 Mar 2020 Shift 2 Paper

© examsiri.com

Question : 56 of 100

Marks: +1, -0

If

a-b=18

and

a^{3}-b^{3}=324

, then find

a b

.

$-102$
103
105
$-104$

Solution:

Given,

a-b=18

and

a^{3}-b^{3}=324

We know,

a^{3}-b^{3}=(a-b)(a^{2}+a b+b^{2})

∴

(a-b)(a^{2}+a b+b^{2})=324

⇒

18 \×(a^{2}-2 a b+b^{2}+3 a b)=324

⇒

(a-b)^{2}+3 a b={324}/{18}=18

⇒

(18)^{2}+3 a b=18

⇒

3 a b=18-324=-306

⇒

a b={-306}/{3}=-102

© examsiri.com

Go to Question:

Prev Question

Next Question