High School Math : Trigonometry

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #3 : The Unit Circle And Radians

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

Possible Answers:

\(\displaystyle \frac{1}{2}\)

\(\displaystyle 1\)

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

\(\displaystyle -1\)

\(\displaystyle \frac{\sqrt{2}}{2}\)

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:

\(\displaystyle 1\)

\(\displaystyle -1\)

\(\displaystyle \frac{2\sqrt2}{2}\)

\(\displaystyle \frac{\sqrt2}{2}\)

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

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 #5 : The Unit Circle And Radians

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

Possible Answers:

\(\displaystyle \frac{\sqrt2}{2}\)

\(\displaystyle -1\)

\(\displaystyle \frac{1}{2}\)

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

\(\displaystyle 1\)

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 #1 : The Unit Circle And Radians

What is \(\displaystyle \sin(\pi)\)?

Possible Answers:

\(\displaystyle \frac{\sqrt{2}}{2}\)

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

\(\displaystyle \frac{1}{2}\)

\(\displaystyle 1\)

\(\displaystyle 0\)

Correct answer:

\(\displaystyle 0\)

Explanation:

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

Example Question #2 : The Unit Circle And Radians

What is \(\displaystyle \cos(\pi)\)?

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle -1\)

\(\displaystyle \frac{\sqrt2}{2}\)

\(\displaystyle \frac{\sqrt3}{2}\)

\(\displaystyle 1\)

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 \(\displaystyle (\pi,-1)\).

Example Question #11 : The Unit Circle And Radians

What is the value of the angle \(\displaystyle \frac{3\pi}{2}\) radians when converted to degrees?

Possible Answers:

\(\displaystyle 270\)

\(\displaystyle 90\)

\(\displaystyle -45\)

\(\displaystyle 135\)

\(\displaystyle -180\)

Correct answer:

\(\displaystyle 270\)

Explanation:

The answer can be found using the conversion of 1 radian equals \(\displaystyle \frac{180}{\pi}\) degrees.  Multiplying \(\displaystyle \frac{3\pi}{2}\) by this conversion factor gives 270 degrees.

Example Question #2 : Understanding Radians And Conversions

A point has Cartesian coordinates \(\displaystyle (1,3)\). Rewrite this as an ordered pair in the polar coordinate plane, rounding the coordinates to the nearest hundredth.

Possible Answers:

\(\displaystyle (3.16,0.80)\)

\(\displaystyle (2.83, 1.25)\)

\(\displaystyle (3.16,0.32)\)

\(\displaystyle (3.16,1.25)\)

\(\displaystyle (2.83, 0.32)\)

Correct answer:

\(\displaystyle (3.16,1.25)\)

Explanation:

Set \(\displaystyle x=1, y=3\). Calculate the polar coordinates \(\displaystyle (r,\theta )\) as follows:

\(\displaystyle r = \sqrt{x^{2}+y^{2}}= \sqrt{1^{2}+3^{2}}=\sqrt{10} \approx 3.16\)

\(\displaystyle \theta = \arctan \frac{y}{x}= \arctan \frac{3}{1} = \arctan 3 \approx 1.25\)

Example Question #3 : Understanding Radians And Conversions

How many degrees are in \(\displaystyle \frac{\pi}{6}\) radians?

Possible Answers:

\(\displaystyle 60^\circ\)

\(\displaystyle 120^\circ\)

\(\displaystyle 45^\circ\)

\(\displaystyle 360^\circ\)

\(\displaystyle 30^\circ\)

Correct answer:

\(\displaystyle 30^\circ\)

Explanation:

\(\displaystyle \frac{x^\circ}{\frac{\pi}{6}}=\frac{180^\circ}{\pi}\)

Cross multiply:

\(\displaystyle x^\circ*\pi=180^\circ*\frac{\pi}{6}\)

Notice that the \(\displaystyle \pi\)'s cancel out:

\(\displaystyle x^\circ=180^\circ*\frac{1}{6}\)

\(\displaystyle x^\circ=30^\circ\)

Example Question #12 : The Unit Circle And Radians

How many radians are in \(\displaystyle 180^\circ\)?

Possible Answers:

\(\displaystyle \frac{\pi}{2}\)

\(\displaystyle 3\pi\)

\(\displaystyle \pi\)

\(\displaystyle 2\pi\)

\(\displaystyle 4\pi\)

Correct answer:

\(\displaystyle \pi\)

Explanation:

The relationship between degrees and radians is \(\displaystyle 180^\circ=\pi\) radians. Therefore, \(\displaystyle 180^\circ\) would be \(\displaystyle \pi\) radians.

Example Question #1 : Understanding Radians And Conversions

Express in radians: \(\displaystyle 125^{\circ }\)

Possible Answers:

\(\displaystyle \frac{2\pi }{3}\)

\(\displaystyle \frac{5\pi }{9}\)

\(\displaystyle \frac{15\pi }{36}\)

\(\displaystyle \frac{11\pi }{18}\)

\(\displaystyle \frac{25\pi }{36}\)

Correct answer:

\(\displaystyle \frac{25\pi }{36}\)

Explanation:

Since \(\displaystyle 180 ^{\circ } = \pi \textrm{ rad}\), we can convert as follows:

\(\displaystyle 125 \cdot \frac{\pi }{180} = \frac{25\pi }{36}\)

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