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if sinx=3/5,cosy=12/13,where x and y both lie in 2nd quadrant, find the value of sin(x+y),cos(x-y),tan(x+y)?

  • maths -

    in QII, cosy is negative
    cosx = -4/5
    siny = 5/13

    now, just plug in the formulas. for example

    sin(x+y) = sinx*cosy+cosx*siny
    = (3/5)(-12/13)+(-4/5)(5/13)
    = -36/65 - 20/65
    = -56/65

  • maths -

    -56/65

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