Can someone explain me these using the unit circle?

cos(180-theta)= -cos theta

cos(-theta)=cos theta

sin(-theta)= -sin theta

Thanks!

Printable View

- Feb 9th 2014, 11:57 AMlaurettarosaAnother Unit circle question
Can someone explain me these using the unit circle?

cos(180-theta)= -cos theta

cos(-theta)=cos theta

sin(-theta)= -sin theta

Thanks! - Feb 9th 2014, 01:15 PMsakonpure6Re: Another Unit circle question
Hello laurettarosa! Are you familiar with the C.A.S.T Rule? Basically, it helps us determine where the trig ratios: sin, cos, and tan are positive or negative.

Let Q = theta.

Attachment 30152

The**C**in**C**AST is located in the**4th**quadrant, and only**C**osine is positive there.

The**A**in C**A**ST is located in the**1st**quadrant and**S**ine,**C**osine, and**T**an are positive there.

The**S**in CA**S**T is located in the**2nd**quadrant and only**S**ine is positive there

The**T**is CAS**T**is located in the**3rd**quadrant and only**T**an is positive there.

Moving on,

cos(180 - Q) : Analysing the angle: 180 - Q, this means that Q is located in the 2nd quadrant and according to CAST, only sine is positive there.

Therefore, cos(180 - Q) = - cos Q

Can you handle the rest? if you have any other questions, please do not hesitate to ask. - Feb 9th 2014, 02:21 PMromsekRe: Another Unit circle question