Use the angle difference identities to find the exact value of the trigonometric expression.

cos 195°

can someone tell me the answer pleasee?

Question

Use the angle difference identities to find the exact value of the trigonometric expression. 

cos 195°

can someone tell me the answer pleasee?

anonymous · Answer

this is what the question is asking you to do, to use the cos of the diffrence of angles...

anonymous · Answer

i'm sorry i dont understand?

ash2326 · Answer

Use A=240
B=45

anonymous · Answer

okay thank you :) one second.

ash2326 · Answer

Use this
$$\cos (A-B)=\cos A \times \cos B+\sin A \times \sin B$$

anonymous · Answer

how do i get sin A and sin B?

anonymous · Answer

just sub the values that @ash produces

anonymous · Answer

this is the formula for cos(A-B)

anonymous · Answer

do you want a proof for that formula...

ash2326 · Answer

$$\sin 240=\sin (180+60)=-\sin 60$$

anonymous · Answer

i get 195 when i do Cos(A-B)

ash2326 · Answer

Yes, but you need to find the value of $\cos 195$
So we use 
$$\cos (A-B)$$
and then we expand it to find the value of cos 195

anonymous · Answer

240-45

anonymous · Answer

im not following. i did (240 -45) and got 195

anonymous · Answer

i don't understand what i'm supposed to do , this is supposed to be an Algebra II course but its trig problems i dont even know what cos and sin is.

ash2326 · Answer

You haven't studied trigonometry, have you?

anonymous · Answer

not at all.

ash2326 · Answer

Oh, then how would you know this? Was this part of your course?

anonymous · Answer

yes , this is my last course before i graduate and it says nothing about any of this in my textbooks so im at a loss.

anonymous · Answer

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