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Math Help - trig identities

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    trig identities

    If sin A=3/5, <A is in quadrant 1, cos B= -5/13, and <B is in quadrant two find:
    sin(A+B)
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    Quote Originally Posted by blame_canada100 View Post
    If sin A=3/5, <A is in quadrant 1, cos B= -5/13, and <B is in quadrant two find:
    sin(A+B)
    for angle A, sketch a reference triangle in quad I ...

    since \sin{A} = \frac{3}{5} , opposite side = 3 , hypotenuse = 5 ... so the adjacent side = 4 ...therefore, \cos{A} = \frac{4}{5}


    sketch another reference triangle in quad II and use the same procedure to find \sin{B} ... remember the side that runs along the x-axis will have a negative value.


    finally, sub in your values into the sum identity for sine ...

    \sin(A+B) = \sin{A}\cos{B} + \cos{A}\sin{B}
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