RRB NTPC Mains or Stage 2 Model Paper 10 with solutions

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Question : 34 of 120

Marks: +1, -0

If tan

A =\text"1 -cosB"/ \text"sinB"

, what is

\text"2tanA "/{1- tan^2 A}

equal to?

tan $B /2$
2 tan B
tan B
4 tan B

Solution:

(c)

{2 tanA} /{1-tan ^2A} =\text"1 -cos 2B" /\text"sin 2B"={1 -(1 -2sin^2 B)}/{2sin cos B}

[∵{cos2B =1 -2sin^2 B and sin 2B =2sin B cosB}]

={sinB}/{cosB }= tan B

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