- #1

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I have to verify this identity and cant seem to figure it out. cos (x-y)=cos x * cos y + sin x * sin y

well since cos y = 0, it kind of eliminates that side of the equation and I end up with sinx * sin1

Did I go about this all wrong?

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- Thread starter silversorrow
- Start date

- #1

- 1

- 0

I have to verify this identity and cant seem to figure it out. cos (x-y)=cos x * cos y + sin x * sin y

well since cos y = 0, it kind of eliminates that side of the equation and I end up with sinx * sin1

Did I go about this all wrong?

- #2

Cyosis

Homework Helper

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It is sin(x)*1 not sin 1, because sin(pi/2)=1. So far you have cos(x-pi/2)=sin(x), which is correct. Now write out the right hand side of your original equation and see what you get.

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