Posted by Trig on Tuesday, November 3, 2009 at 8:27pm.
How come cosine of 225 degrees is a positive number i thought it was negative because it's reference angle would be 45 degrees below the second quadrant and in a unit circle cosine is just the x value so I thought cosine of something in both the second and third were negative
apparently i'm wrong please explain

Trig  Reiny, Tuesday, November 3, 2009 at 8:33pm
225º is in the fourth quadrant, 45º below the first quadrant, so its x value is indeed positive.
Check how angles are measured.

Trig  Trig, Tuesday, November 3, 2009 at 8:34pm
I think i was in radians my bad
um how come tan of 300 is negative root three
tangent in unit circle is y/x I am getting .5/(root three/2)
which is not root three

OOPS Trig  Reiny, Tuesday, November 3, 2009 at 8:36pm
Forget about my previous post.
Obviously 225º is in the third quadrant, 45º below the second quadrant like you said.
So of course cos 225 is negative.

Trig  Reiny, Tuesday, November 3, 2009 at 8:38pm
tan 300º
= tan 60º by the CAST rule
= √3/1 from the ratios of the 306090 triangle
= √3

Trig  Trig, Tuesday, November 3, 2009 at 8:44pm
why wouldn't you use the 30 degree angle?
I did 360 90 to get 270 degrees and then did 300  270 to get 30 degrees and used that angle why would I use the 60 degree angle instead of the thirty

Trig  Reiny, Tuesday, November 3, 2009 at 9:03pm
Always ask yourself,
"How far away from the xaxis am I "?
to get the reference angle.
e.g. sin 160
160º is 20º away from the xaxis and according to the CAST rule in quadrant II the sine is positive, so
sin 160º
= sin 20º
e.g. tan 310º
310º is 50º from the xaxis and according to the CAST rule, in quadrant IV the tangent is negative, so
tan 310
= tan 50
check my examples with your calculator
Answer This Question
Related Questions
 Algebra2  1. An artist is designing triangular mirrors. Determine the number...
 Algebra 2 ..  1. An artist is designing triangular mirrors. Determine the ...
 Algebra 2....  1. An artist is designing triangular mirrors. Determine the ...
 math  use the unit circle to determine the exact value of each angle: sine 30 ...
 Spherical Trigonometery  I am trying to apply the formula cos c = cos a x cos b...
 Trig  I'm confused on how to determine what the end result angles are for a ...
 trig help  I need help finding sinA if cosA=(3/5) and A is greater than 90 ...
 trig identities  cos94 degrees cos18 degrees+ sin94 degrees sin18 degrees. ...
 math  If the angle of declination is known, a surveyor would use_______ to find...
 Trigonometry  I had to find the sine, cosine and tangent of 150 degrees. I got...
More Related Questions