posted by Trig on .
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
225º is in the fourth quadrant, 45º below the first quadrant, so its x value is indeed positive.
Check how angles are measured.
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
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.
= -tan 60º by the CAST rule
= -√3/1 from the ratios of the 30-60-90 triangle
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
Always ask yourself,
"How far away from the x-axis am I "?
to get the reference angle.
e.g. sin 160
160º is 20º away from the x-axis and according to the CAST rule in quadrant II the sine is positive, so
= sin 20º
e.g. tan 310º
310º is 50º from the x-axis and according to the CAST rule, in quadrant IV the tangent is negative, so
= -tan 50
check my examples with your calculator