SSC CHSL Model Paper 5

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Question : 45 of 100

Marks: +1, -0

The least value of

3^x + 3^{-x}

is :

2
1
0
$2/3$

Solution:

Let

A = 3x

and

1/A=3^{-x}

⇒ Both are positive.
Now, A.M . of A and

1/A

is greater than or equal to their G.M.
i.e.

{A/1/A}/2≥√{A . 1/A}

or

A+1/A≥2

or

3^x + 3^{-x}≥2

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