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trig

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how do i find cosX if i am given sin x= -4/5 and tan <o???

  • trig -

    Isn't the sine negative in the III and IV quadrants, and isn't the tangent negative in the II and IV quadrant.
    So clearly our angle x must be in IV

    Make a triangle using sinx = 4/5
    The third side (the adjacent) would be 3 and cosx = 3/5, but we are in quadrant IV, and in IV the cosine is positive, so ..
    cosx = 3/5

  • trig -

    cos^2x+ sin^2 x=1

    the tangent being negative tells you which of the two answers is correct.

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