Solve cosxcos(-x) - sinxsin(-x) = 1

1. Dec 8, 2007

ravey_dotson

cosxcos(-x) - sinxsin(-x) = 1

I know I'm making it harder than it is, but I can't seem to figure it out.
Any help would be appreciated.

RaveN

2. Dec 8, 2007

Dick

cos(-x)=cos(x). sin(-x)=-sin(x).

3. Dec 8, 2007

ravey_dotson

When I plugged those in then I get cosx2 - sinx2 = 1 and then I get completely lost.

4. Dec 8, 2007

Dick

When I plug them in I get cos(x)^2+sin(x)^2=1. There are two minus signs associated with the sin(x)^2.

5. Dec 8, 2007

ravey_dotson

Because it's -sin to begin with. I knew I was making it too hard. Thanks.

6. Dec 8, 2007

Hurkyl

Staff Emeritus
Another way: isn't the l.h.s. in the form of an angle addition formula?

7. Dec 8, 2007

HallsofIvy

Staff Emeritus
Not with the correct signs! It's cos2(x)+ sin2(x)!

8. Dec 8, 2007

Dick

It is cos(x+(-x)). That is another way to do it.