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If cos⁡x = −35\frac{-3}{5}5−3​ and x lies in the third quadrant, then the value of the sin x is:
Question

If cos⁡x = 35\frac{-3}{5} and x lies in the third quadrant, then the value of the sin x is:

A.

4/5

B.

1

C.

0

D.

-4/5

Correct option is D

Given:

cosx=35,\cos x = -\frac{3}{5},​ , x  lies in the third quadrant.

Formula Used:

sin2x+cos2x=1\sin^2 x + \cos^2 x = 1​​

Solution:

sin2x=1cos2x\sin^2 x = 1 - \cos^2 x​​

sin2x=1(35)2 sin2x=1925 sin2x=2525925=1625 sinx=45(x lies in third quadrant)\sin^2 x = 1 - \left( -\frac{3}{5} \right)^2\\\ \sin^2 x = 1 - \frac{9}{25}\\\ \sin^2 x = \frac{25}{25} - \frac{9}{25} = \frac{16}{25}\\\ \\\sin x = -\frac{4}{5}\quad \quad \text{(x lies in third quadrant)}​​

Therefore, the value of sin x is  -4/5.

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