how to solve? (1 Viewer)

[kasser]

sin identities in attachment

 

[kev-kun]

Draw two separate triangles for sin(a) and sin(b). Use pythagoras to find the last side. Expand the sin(a+b) and after that its just a matter of substitution.

 

[Squar3root]

draw a triangle such that sina = 4/5 and another triangle such that sinb = 5/13


sin(a + b) = sin a cos b + sin b cos a

now read the values from the triangles and sub them in above

my answer was 63/65