SSC CGL Tier II 12 Apr 2015 Paper

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Question : 55 of 100

Marks: +1, -0

The value of

√{72+√{72+√{72+... . .}}}

is

9
8
18
12

Solution:

(1)

x=√{72+√{72+√{72+... . .}}}

On squaring both sides,

x=72√{72+√{72+√{72+... . .}}}

⇒

x^{2}=72+x

⇒

x^{2}-x-72=0

⇒

x^{2}-9 x+8 x-72=0

⇒

x(x-9)+8(x-9)=0

⇒

(x+8)(x-9)=0

⇒

x = 9

because

x ≠ 8

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