hello again!

ok, so here's a problem where it asks to change the equation so that "only one trigonometric ratio is present."

the equation is...

now, i'm only aware of one trig. identity that explains sin in terms of cos and it is called a half-angle identity.

and it looks like this...

Is this the identity i would use so that only one trig. ratio is present?

if so, could i just say...

or maybe...