[High School - Math] Trigonometry

[Cosmic M]

Re: [High School - Trig]

well, the test is tommorow, wish me luck.

[180digi]

Re: [High School - Math] Trigonometry

I'd like to pose a question involving trigonometry without creating a new topic if that is quite acceptable. A study question in my textbook says,

"...find the point (x,y) on the unit circle that corresponds to the real number t.

43.) t = 2(pi)/3

I know that the point is (-1/2, radical3/2), but is there any way to find this out without looking at a unit circle? We're being quizzed on this soon, and I'm not sure if we are going to be provided a unit circle for reference. Thanks.

[masamursha]

Re: [High School - Math] Trigonometry

the unit circle is just showing you that the hypotenuse of that triangle will always be 1. You don't have to draw the circle, you could just draw the triangle where the hypotenuse is 1 on the coordinate plane. Drawing it on the coordinate plane will just help you make sure that you are in the right quadrant.

[GuidoHunter]

Re: [High School - Math] Trigonometry

2pi = 360 degrees
2pi/3 = 120 degrees

That's in the second quadrant.

sin(120 degrees) = root(3)/2
cos(120 degrees) = -1/2

Or, since 120 degrees makes a 60 degree angle with the horizontal, you could just do sin(60) and cos(60), then just remember to make the x coordinate negative, what with cosines being negative in the second quadrant.

Now, if you don't know the sines and cosines of common angle measures, you're in trouble for any trig problem, so commit the sines, cosines, and tangents of 0, pi/6, pi/4, pi/3, and pi/2 to memory ASAP.

--Guido

http://andy.mikee385.com

[180digi]

Re: [High School - Math] Trigonometry

Let me just make sure I understand this. I'll do a problem.

5.) t=pi/4

pi/4 x 180º/pi = 45º. I drew this triangle.



SOA-CAH-TOA, so it's (1/rad2, 1/rad2).

1/rad2 x rad2/rad2 = rad2/2

the point on the unit circle is (rad2/2, rad2/2)

[dore]

Re: [High School - Math] Trigonometry

Just memorize the unit circle. You'll reference it for the rest of your math career so you ought to learn it now.

[masamursha]

Re: [High School - Math] Trigonometry

yup you got it 180digi