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March 30, 2017

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Angle a lies in the second quadran and angle b lies in the third quadrant such that cos a = -3/5 and tan b = 24/7. Determine an exact value for cos (a+b), sin(a-b)

  • maths - ,

    sin a = 4/5
    sin b = -24/25
    cos b = -7/25

    cos(a+b) = cosa*cosb-sina*sinb
    = (-3/5)(-7/25) - (4/5)(-24/25)
    = 21/125 + 96/125
    = 117/125

    now apply the formula for sin(a-b) the same way.

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