Trig

[lilchinoboy03]

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((sin^2👍 - cos^2👍)(sin^2👍 + cos^2👍)) / sin2y = -cos(2y)/sin(2y) = -cot(2y)

So I get the cotangent part, but i dont get how the nominator turns into -cos(2y). So sin squared plus cos squared = 1. and you're left with sin squared - cos squared. does this equal negative cos 2 theta???

 

[Streetwolf]

((sin^2👍 - cos^2👍)(sin^2👍 + cos^2👍)) / sin2y = -cos(2y)/sin(2y) = -cot(2y)

So I get the cotangent part, but i dont get how the nominator turns into -cos(2y). So sin squared plus cos squared = 1. and you're left with sin squared - cos squared. does this equal negative cos 2 theta???

cos(s+t) = cos(s)cos(t) - sin(s)sin(t)

cos(2x) = cos(x+x) = cos(x)cos(x) - sin(x)sin(x) = cos^2(x) - sin^2(x)
So -cos(2x) = - (cos^2(x) - sin^2(x)) = sin^2(x) - cos^2(x)