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I have to rearrange Equation(1) to make Equation(2) using trigonometric identities

(1): E(θ)=2Eo + (ΔR)^2 (c(x)cos^2(θ-θo) + c(y)sin^2(θ-θo))

(2): E(θ)=2Eo + ½(ΔR)^2 ((c(x)-c(y))cos(2(θ-θo)) + (c(x) + c(y))

I was able to get everything withing the bracket in Equation(2) but i cannot figure out how it changes from (ΔR)^2 to ½(ΔR)^2 ?

(btw: when it says Eo I mean E sub 0 and θ sub 0, when I say c(x) or c(y) I really mean c sub x, also by ^2 i mean squared of course))

I really hope someone can help me out here!!!!:shy:

Also I used the Identity:

cos^2(θ-θo) --> ½(1+cos2(θ-θo))

and

sin^2(θ-θo) --> ½(1-cos2(θ-θo))

for '(θ-θo)' I just use something easier like A for example, anyways like i said i cannot understand the ½(ΔR)^2 in the 2nd equation!