How do you evaluate #sin (tan^-1(1/4) + cos^-1(-2/3))#?
So, the angle a is either in the 1st quadrant or in the 3rd.
sin a = +-1/sqrt 17 and cos a = +-4/sqrt 17#.
So, the angle b is either in the 2nd quadrant or in the 3rd.
Now, the given expression is
sin (a + b ) = sin a cos b + cos a sin b