Find sin (x + y)
Angle x is acute, angle y is obtuse, cos x = 15/17
and sin y = 3/5. Find sin (x + y).
After doing the math, I found sin (x + y) to be 77/85.
The textbook tells me that the answer is 13/85.
I know 13/85 would be the answer if we were looking for
sin (x MINUS y), right?
sin(x+y) = sin(x)cos(y) +sin(y)cos(x)
Since angle y is a second quadrant angle cos(y)< 0 so you use cos(y) = -4/5 instead of 4/5
sin(x+y) = (-32+45)/85
I now see what I did wrong. Thanks.
Originally Posted by Calculus26