High School Math : The Unit Circle and Radians

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #1 : The Unit Circle And Radians

What is \displaystyle \sin(\frac{\pi}{2})?

Possible Answers:

\displaystyle -1

\displaystyle \frac{\sqrt2}{2}

\displaystyle 2\pi

\displaystyle 0

\displaystyle 1

Correct answer:

\displaystyle 1

Explanation:

If you examine the unit circle, you'll see that the the \displaystyle \sin(\frac{\pi}{2})=1. If you were to graph a sine function, you would also see that it crosses through the point \displaystyle (\frac{\pi}{2},1).

Example Question #2 : The Unit Circle And Radians

What is \displaystyle \cos(\frac{2\pi}{3})?

Possible Answers:

\displaystyle 0

\displaystyle -\frac{1}{2}

\displaystyle \frac{1}{2}

\displaystyle 1

\displaystyle -1

Correct answer:

\displaystyle -\frac{1}{2}

Explanation:

If you look at the unit circle, you'll see that \displaystyle \cos(\frac{2\pi}{3})=\frac{1}{2}. You can also think of this as the cosine of \displaystyle 60^\circ, which is also \displaystyle \frac{1}{2}.

Example Question #1 : Using The Unit Circle

What is \displaystyle \sin(\frac{2\pi}{3})?

Possible Answers:

\displaystyle \frac{1}{2}

\displaystyle -1

\displaystyle 0

\displaystyle -\frac{\sqrt3}{2}

\displaystyle \frac{\sqrt3}{2}

Correct answer:

\displaystyle \frac{\sqrt3}{2}

Explanation:

If you look at the unit circle, you'll see that \displaystyle \sin(\frac{2\pi}{3})=\frac{\sqrt3}{2}. You can also think of this as the sine of \displaystyle 60^\circ, which is also \displaystyle \frac{\sqrt3}{2}.

Example Question #3 : The Unit Circle And Radians

What is \displaystyle \cos(\frac{\pi}{4})?

Possible Answers:

\displaystyle \frac{\sqrt2}{2}

\displaystyle \frac{2\sqrt2}{2}

\displaystyle \frac{1}{2}

\displaystyle 1

\displaystyle 0

Correct answer:

\displaystyle \frac{\sqrt2}{2}

Explanation:

Using the unit circle, \displaystyle \cos(\frac{\pi}{4})=\frac{\sqrt2}{2 }. You can also think of this as the cosine of \displaystyle 45^\circ, which would also be \displaystyle \frac{\sqrt2}{2}.

Example Question #3 : The Unit Circle And Radians

What is \displaystyle \cos(\frac{\pi}{2})?

Possible Answers:

\displaystyle \frac{1}{3}

\displaystyle \frac{\sqrt2}{}2

\displaystyle 1

\displaystyle -1

\displaystyle 0

Correct answer:

\displaystyle 0

Explanation:

Using the unit circle, you can see that \displaystyle \cos(\frac{\pi}{2})=0. If you were to graph a cosine function, you would also see that it crosses through the point \displaystyle (\frac{\pi}{2},0).

Example Question #4 : The Unit Circle And Radians

What is \displaystyle \sin(\frac{3\pi}{4})?

Possible Answers:

\displaystyle 1

\displaystyle \frac{\sqrt{2}}{2}

\displaystyle -1

\displaystyle \frac{-\sqrt2}{2}

\displaystyle \frac{1}{2}

Correct answer:

\displaystyle \frac{\sqrt{2}}{2}

Explanation:

Using the unit circle, \displaystyle \sin(\frac{3\pi}{4})=\frac{\sqrt2}{2 }. You can also think of this as the sine of \displaystyle 135^\circ, which would also be \displaystyle \frac{\sqrt2}{2}.

Example Question #4 : The Unit Circle And Radians

What is \displaystyle \cos (\frac{3\pi}{4})?

Possible Answers:

\displaystyle \frac{2\sqrt2}{2}

\displaystyle -\frac{\sqrt2}{2}

\displaystyle 1

\displaystyle \frac{\sqrt2}{2}

\displaystyle -1

Correct answer:

\displaystyle -\frac{\sqrt2}{2}

Explanation:

Using the unit circle, you can see that the \displaystyle \cos (\frac{3\pi}{4})=-\frac{\sqrt2}{2}. Since the angle is in Qudrant II, sine is positive and cosine is negative.

Example Question #2 : The Unit Circle And Radians

What is \displaystyle \sin(\frac{\pi}{4})?

Possible Answers:

\displaystyle \frac{\sqrt2}{2}

\displaystyle \frac{1}{2}

\displaystyle 1

\displaystyle -\frac{\sqrt2}{2}

\displaystyle -1

Correct answer:

\displaystyle \frac{\sqrt2}{2}

Explanation:

Using the unit circle, \displaystyle \sin(\frac{\pi}{4})=\frac{\sqrt2}{2 }. You can also think of this as the sine of \displaystyle 45^\circ, which would also be \displaystyle \frac{\sqrt2}{2}.

Example Question #21 : Graphing The Sine And Cosine Functions

What is \displaystyle \sin(\pi)?

Possible Answers:

\displaystyle \frac{\sqrt{2}}{2}

\displaystyle \frac{\sqrt{3}}{2}

\displaystyle 0

\displaystyle 1

\displaystyle \frac{1}{2}

Correct answer:

\displaystyle 0

Explanation:

If you examine the unit circle, you'll see that that \displaystyle \sin(\pi)=0

Example Question #22 : Graphing The Sine And Cosine Functions

What is \displaystyle \cos(\pi)?

Possible Answers:

\displaystyle 1

\displaystyle 0

\displaystyle \frac{\sqrt3}{2}

\displaystyle -1

\displaystyle \frac{\sqrt2}{2}

Correct answer:

\displaystyle -1

Explanation:

If you examine the unit circle, you'll see that the value of \displaystyle \cos(\pi)=-1. You can also get this by examining a cosine graph and you'll see it crosses the point \displaystyle (\pi,-1).

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