Question

Find the value of cos{2 tan^-1(-7)}
​

Answer 1

answer of this question

Answer 2

Step-by-step explanation:

sin(4cot

−1

3)

Let tan

−1

[

7

1

]=θ

⇒tanθ=

7

1

⇒cosθ=

50

7

We need cos2θ, which is 2cos

2

θ−1.

∴cos2θ=2×

50

49

−1=

25

24

Now, in the first option, let cot

−1

3 be α.

⇒sinα=

10

1

and cosα=

10

3

sin4α=2sin2αcos2α

sin4α=2×2×

10

1

×

10

3

×(2×

10

9

−1)

sin4α=

10

12

×

10

8

=

100

96

=

25

24