Hello, iiharthero!
Prove: .
Used compound-angle formulae except seemed to only get up to:
. . . . This is correct -- Good work!
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Got it?
cos(x+y) x cos(x-y) = cos squared y - sin squared x
= cos squared x - sin squared y
used double angle formulae except seemed to only get up to
cossquaredx cossquared y - sin squared x sin squared y ??
any help is GREATLY APPRECIATED
thankss !!