Trigonometry Identities/Equations

[delish_fish]

Simplify the following expressions.

a. cos(180° + x) + cos(180° - x)

b. cos(126°)cos(36°) + sin(126°)sin(36°)


I honestly have NO clue where to begin with either of these questions. There are steps in my notes but I just don't understand them at all. Could anyone provide me with simpler/easier steps to solve these types of equations???

THANK YOU!

 

[Deleted member 4993]

Simplify the following expressions.

a. cos(180° + x) + cos(180° - x)

b. cos(126°)cos(36°) + sin(126°)sin(36°)


I honestly have NO clue where to begin with either of these questions. There are steps in my notes but I just don't understand them at all. Could anyone provide me with simpler/easier steps to solve these types of equations???

THANK YOU!

You need to have a face-to-face talk with your teacher - since you cannot understand your class-notes.

We cannot see your class notes - so really cannot provide a comparatively simpler explanation.

As a starting point - can you tell us:

Cos (A + B) = ??

Sin (A + B) = ??

and

Cos(180°) = ??

 

[delish_fish]

She told me, to use the sum/difference formula. And sub the value in by using the unit circle.
She then told me that I can use the cos(theta+beta) formula for cos(180+x) where theta=180 and beta=x
and for the cos(180-x) she told me to use cos(theta-beta) formula where theta=180 and beta=x
Then she said to use the unit circle to sub the values cos(180) and sin(180)

Where did she get sin from and what's a unit circle???? And is there any explanation for the sum/difference formula?????
In the notes, it shows that the sum/difference formula but it doesn't explain how to use it.
And the explanation of the unit circle is not in notes at all. I've read through them several times over and over again and I'm VERY lost.

 

[Aladdin]

Where did she get sin from and what's a unit circle???? And is there any explanation for the sum/difference formula?????
VERY lost.

Sum/difference formulas.

sin(A+B)=sin A cos B + cos A sin B
sin(A-B)=sin A cos B - cos A sin B
cos(A+B)=cos A cos B - sin A sin B
cos(A-B)=cos A cos B + sin A sin B

Well , What does cos(180) equals ...

 

[delish_fish]

Well, I don't understand the sum/difference formulas and what cos 180 equals.
It doesn't give anything in the notes.
And my teacher doesn't even help with it.

 

[Deleted member 4993]

Well, I don't understand the sum/difference formulas and what cos 180 equals.
It doesn't give anything in the notes.
And my teacher doesn't even help with it.

You are not ready for this class....