where does the cos⁡(θ)=1−2sin2(θ2) come from?

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Johnny Cummings · Accepted Answer

It&#039;s a special case of the compound-angle formula cos⁡(A+B)=cos⁡Acos⁡B−sin⁡Asin⁡B. Take A=B=θ2 so cos⁡θ=cos2θ2−sin2θ2. This can be written in two equivalent forms using cos2θ2+sin2θ2=1, one being 1−2sin2θ2 (the other is 2cos2θ2−1)

eris0cg · Accepted Answer

cos⁡(2θ)=1−2sin2(θ)  Change θ→θ2

where does the cos⁡(θ)=1−2sin2(θ2) come from?

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