math
posted by unknown .
tan theta= 15/8 and pi< theta<3pi/2
a. Sin( theta)
b. cos2theta
c. sin( theta  3pi/4)
d. cos(theta/2)
can someone explain to me how do you find the exact value for these?

the angle is in the 3rd quadrant.
So, draw a diagram where the hypotenuse extends down to the left from (0,0)
Since tan = y/x, this means that y = 15 and x = 8. So the hypotenuse of your triangle goes from (0,0) to (8,15), length=17
Now you are ready to go.
sin theta = y/h = 15/17
cos theta = x/h = 8/17
Use these values in your doubleangle, halfangle, and sum/difference formulas.