How would I do this:

-cos(90-x)

I know you would use the compound angle formula and I know how to do it but when you have -cos do you replace the cos with the negative?

so for example

-cos90(-cosx) + sinx(sin90)

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1. co-sine means sine of co-mplimentary angle.

so, cos(90-x) = sin(x)
and your function is just -sin(x)

Or, you can apply the difference formula, but that is done before the negative

-[cos(90-x)]
= -[cos90cosx+sin90sinx]
= -sinx

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posted by Steve

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