since cosb < 0, b is in QII, so
sina = 4/5
cosa = 3/5
sinb = 5/13
cosb = -12/13
Now just evaluate
ain(a+b) = sina cosb + cosa sinb
Use the given information to evaluate sin (a+b). Exact answers only. No decimals.
Tan a = 4/3, cos b ='-12/13; neither a nor b are in quadrant III.
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