Solve Trig Quadrant Help: cos(-65°)

[Krypto78]

Homework Statement

Determine the following and state quadrant.

cos(-65°)

Homework Equations

I make this the 2nd quadrant.

The Attempt at a Solution

where:-
-cos(180 - θ)
-cos ( 180 - (-65))
-cos245
= 0.423

however i wasnt sure if it lied in the 4th quadrant
so:-
-cos(360 - θ)
-cos ( 360 - (-65))
-cos425
= 0.423

Can anyone help me understand this PPPPUUUUURRRRRRLEASE.

Thanks guys.

 

[Mentallic]

This will be an easy one to answer if you know how the angles move.

Basically you start on the positive x-axis and travel in a circle in a counter-clockwise fashion. So at 10^o you'll be in the 1^st quadrant and very close to the x-axis. At 45^o you're half way between the x-axis and y-axis in the 1^st quadrant. At 90^o you're now on the positive end of the y-axis. You continue to move counter-clockwise and now you've hit the 2^nd quadrant.

Negative angles however are defined as starting at the same point on the x-axis but instead you now move clockwise, so at -10^o you're suddenly in the 4^th quadrant.

 

[Krypto78]

Sorry for the late response.

Thank you for the reply all sorted now thanks to ya:)

 

[HallsofIvy]

So you have realized that -65° is in the fourth quadrant, not the second?

 

[Krypto78]

Yes i got there in the end. Problem is I am doing a self study course and the notes are horrific. Wish i had knuckled down when education was free.

Thanks:)