SSC CHSL 15 Oct 2020 Shift 3 Paper

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Question : 59 of 100

Marks: +1, -0

If

2 a+3 b=8

and

a b=5

, then find the value of

4 a^{2}+9 b^{2}

.

2
4
8
6

Solution:

Given,

2 a+3 b=8

On squaring both sides, we get

(2 a+3 b)^{2}=(8)^{2}

⇒

4 a^{2}+9 b^{2}+2 ×2 a ×3 b=64

⇒

4 a^{2}+9 b^{2}+12 a b=64

⇒

4 a^{2}+9 b^{2}=64-12 ×5

[\∵

Given,

a b=5]

⇒

4 a^{2}+9 b^{2}=64-60=4

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