Question 1174754
Find sin(2a) when a terminates in quadrant II. cosa=-4/5. (I got -24/25, but I am not sure if I solved it correctly)
<pre>You are CORRECT!
This is one of the PYTHAG TRIPLES, of the 3-4-5 variety.
And, with  {{{matrix(1,3, cos (a), "=", - 4/5)}}}, OPPOSITE = y = 3 (Quadrant 2), and {{{matrix(1,7, sin (a), "=", O/H, "=", y/r, "=", 3/5)}}}
We now get: {{{highlight_green(matrix(4,3, sin (2a), "=", 2 sin (a) cos (a), sin (2a), "=", 2(3/5)(- 4/5), sin (2a), "=", (6/5)(- 4/5), sin (2a), "=", - 24/25))}}}