Using Compounded Angle Identities: How to Simplify cos(\pi-x) = -cosX?

[moe11]

Homework Statement

cos($$\pi$$-x)= -cosX

the formula is cos(A-b) = cosAcosB+sinAsinB
so i sub in the given to get..
cos$$\pi$$cosx + sin$$\pi$$sinX

then where do i go from there? I am new to math like this, its a much higher level than what I am used to, any help would be very apprieciated. thanks.

Homework Equations

The Attempt at a Solution

 

[rock.freak667]

What does cos(pi) and sin(pi) work out to be?

 

[moe11]

What does cos(pi) and sin(pi) work out to be?

sinpi= 0.054803665
cospi= 0.998497149

i don't know where to go from there, i know after the dust settles i need to have -cosx somehow.

 

[Hurkyl]

Those should be values you have memorized...

(And incidentally, you left your calculator in degree mode on accident)

 

[Mentallic]

Are you familiar with radians? $$\pi =180^o$$

 

[Дьявол]

You can use both radians and degrees. If you use the radian mode you will write π = 3.141592 and if you use degree mode you will write п = 180^o. Anyway, you will get same value. But these values are so easy to remember (even you don't need to remember it, just draw a circle in coordinate system, and remember the x-axis is cos and the y-axis is sin). Now turn for 180^o from 0^o and you will get what?

Regards.