SSC CHSL 12 Oct 2020 Shift 3 Paper

© examsiri.com

Question : 55 of 100

Marks: +1, -0

If

2 x+y=6

and

x y=4

, then find the value of

8 x^{3}+y^{3}

.

48
16
72
64

Solution:

2 x+y=6

(given)
Un cubing both sides, we get
⇒

(2 x+y)^{3}=216

[\∵(a+b)^{3}=a^{3}+b^{3}+3 a b(a+b)]

⇒

8 x^{3}+y^{3}+3(2 x)(y)(2 x+y)=216

(\∵2 x+y=6, x y=4)

⇒

8 x^{3}+y^{3}+3 \×2 \×(4) \×(6)=216

⇒

8 x^{3}+y^{3}+144=216

⇒

8 x^{3}+y^{3}=216-144

∴

8 x^{3}+y^{3}=72

© examsiri.com

Go to Question:

Prev Question

Next Question