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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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