To simplify these expressions, we can use trigonometric identities.

sin(2a)/sin(a) = 2sin(a)cos(a)/sin(a) = 2cos(a)

sin(2a)/(2cos(a)) = sin(2a)/2cos(a) = (2sin(a)cos(a))/(2cos(a)) = sin(a)

sin(2a)/(cos^2(a) - sin^2(a)) = 2sin(a)cos(a)/((cos(a))^2 - (sin(a))^2) = 2sin(a)cos(a)/(cos(2a)) = sin(2a)

So, the simplified expressions are: