SSC CGL 30 Aug 2015 Paper

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Question : 122 of 200

Marks: +1, -0

If cos x +

cos^2

x = 1, then

sin^8x + 2 sin^6x + sin^4x

is equal to

0
3
2
1

Solution:

cos x +

cos^2

x = 1
⇒ cos x = 1 –

cos^2

x
=

sin^2

x ....... (i)
∴

sin^8

x + 2

sin^6

x +

sin^4

x
=

(sin^4 x + sin^2 x)^2

=

((cos x)^2 + sin^2 x)2

=

(cos^2x + sin^2 x)^2

= 1

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