math

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if sin(theta)=1/4
and pie/2<theta<pie what is the value of cos(theta)

  • math -

    make a rough sketch of a right-angled triangle in the second quadrant with a hypotenuse of 4 and a vertical leg of 1.
    (remember sin(angle) = opposite/hypotenuse)

    by Pythagoras, the other side must be √15

    in the second quadrant the cosine is negative, so
    cos(theta) = -√15/4

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