SSC CHSL Model Paper 1

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Question : 41 of 100

Marks: +1, -0

If

3 ^x + 27(3 ^{-x}) = 12

, then what is the value of x ?

4
3
1 or 2
0 or 1

Solution:

Given,

3 ^x + 27(3 ^{-x}) = 12

Let

3^x=y

∴

y+27/y=12

⇒

y^2- 12y+27 = 0

⇒

y^2 -9 y -3 y + 2 7 = 0

⇒

(y -3)(y- 9) = 0 ⇒ y = 3,9

when y = 3;
⇒

3^x=3

∴

x=1

when y = 9
⇒

3^x= 9

∴

x=2

x = 1,2 are value of x.

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