posted by sarah .
if sin where defined=1/5 and where defined is in quadrant I find the exact value of sin2 where defined
make a diagram and use Pythagoras to find the third side x
x^2 + 1^2 = 5^2
x = sqrt(24)
so cos(theta)= sqrt(24)/5
sin(2theta) = 2sin(theta)cos(theta)