Question

1-1/2 sin(2theta) complete identity

Answer 1

Howdy, Dee,
What you're presenting here is not (yet) an identity. So I'd modify your problem statement to read as follows: "Use one or more trig identities to rewrite 1-(1/2)sin(2*theta) as a new trig identity."

It happens that sin(2 theta) = 2 * sin (theta) * cos (theta). Try substituting this result into the expression you've presented.