You can put this solution on YOUR website! find the exact value of the trigonometric function,
cos(u+v) = cos(u)cos(v)-sin(u)sin(v)
======
sin(u) = 5/13
cos[sqrt(13^2-5^2)]/13 = 12/13
Note: This implies that u is in QI
----------------------------------
cos(v) = -3/5
sin(v) = sqrt(25-9)/5 = 4/5
Note: This implies that v is in QII
===============================
cos(u+v) = cos(u)cos(v)-sin(u)sin(v)
= (12/13)(-3/5) - (5/13)(4/5)
======
= (-36 - 20)/65
------
= -56/65
------
= -0.8615
===================
Cheers,
Stan H.
===================
(