# 5.2 Unit circle: sine and cosine functions  (Page 8/12)

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$\mathrm{sin}\text{\hspace{0.17em}}\frac{\pi }{2}$

$\mathrm{sin}\text{\hspace{0.17em}}\frac{\pi }{3}$

$\frac{\sqrt{3}}{2}$

$\mathrm{cos}\text{\hspace{0.17em}}\frac{\pi }{2}$

$\mathrm{cos}\text{\hspace{0.17em}}\frac{\pi }{3}$

$\frac{1}{2}$

$\mathrm{sin}\text{\hspace{0.17em}}\frac{\pi }{4}$

$\mathrm{cos}\text{\hspace{0.17em}}\frac{\pi }{4}$

$\frac{\sqrt{2}}{2}$

$\mathrm{sin}\text{\hspace{0.17em}}\frac{\pi }{6}$

$\mathrm{sin}\text{\hspace{0.17em}}\pi$

0

$\mathrm{sin}\text{\hspace{0.17em}}\frac{3\pi }{2}$

$\mathrm{cos}\text{\hspace{0.17em}}\pi$

−1

$\mathrm{cos}\text{\hspace{0.17em}}0$

$\mathrm{cos}\text{\hspace{0.17em}}\frac{\pi }{6}$

$\frac{\sqrt{3}}{2}$

$\mathrm{sin}\text{\hspace{0.17em}}0$

## Numeric

For the following exercises, state the reference angle for the given angle.

$240°$

$60°$

$-170°$

$100°$

$80°$

$-315°$

$135°$

$45°$

$\frac{5\pi }{4}$

$\frac{2\pi }{3}$

$\frac{\pi }{3}$

$\frac{5\pi }{6}$

$\frac{-11\pi }{3}$

$\frac{\pi }{3}$

$\frac{-\text{\hspace{0.17em}}7\pi }{4}$

$\frac{-\pi }{8}$

$\frac{\pi }{8}$

For the following exercises, find the reference angle, the quadrant of the terminal side, and the sine and cosine of each angle. If the angle is not one of the angles on the unit circle, use a calculator and round to three decimal places.

$225°$

$300°$

$60°,$ Quadrant IV, $\text{sin}\left(300°\right)=-\frac{\sqrt{3}}{2},\mathrm{cos}\left(300°\right)=\frac{1}{2}\text{\hspace{0.17em}}$

$320°$

$135°$

$45°,$ Quadrant II, $\text{\hspace{0.17em}}\text{sin}\left(135°\right)=\frac{\sqrt{2}}{2},$ $\text{\hspace{0.17em}}\mathrm{cos}\left(135°\right)=-\frac{\sqrt{2}}{2}$

$210°$

$120°$

$60°,$ Quadrant II, $\text{\hspace{0.17em}}\text{sin}\left(120°\right)=\frac{\sqrt{3}}{2},$ $\text{\hspace{0.17em}}\mathrm{cos}\left(120°\right)=-\frac{1}{2}$

$250°$

$150°$

$\text{\hspace{0.17em}}30°,$ Quadrant II, $\text{\hspace{0.17em}}\text{sin}\left(150°\right)=\frac{1}{2},$ $\text{\hspace{0.17em}}\mathrm{cos}\left(150°\right)=-\frac{\sqrt{3}}{2}$

$\frac{5\pi }{4}$

$\frac{7\pi }{6}$

$\frac{\pi }{6},$ Quadrant III, $\text{\hspace{0.17em}}\text{sin}\left(\frac{7\pi }{6}\right)=-\frac{1}{2},$ $\text{cos}\left(\frac{7\pi }{6}\right)=-\frac{\sqrt{3}}{2}$

$\frac{5\pi }{3}$

$\frac{3\pi }{4}$

$\frac{\pi }{4},$ Quadrant II, $\text{\hspace{0.17em}}\text{sin}\left(\frac{3\pi }{4}\right)=\frac{\sqrt{2}}{2},$ $\text{\hspace{0.17em}}\mathrm{cos}\left(\frac{4\pi }{3}\right)=-\frac{\sqrt[]{2}}{2}$

$\frac{4\pi }{3}$

$\frac{2\pi }{3}$

$\frac{\pi }{3},$ Quadrant II, $\text{\hspace{0.17em}}\text{sin}\left(\frac{2\pi }{3}\right)=\frac{\sqrt{3}}{2},$ $\text{\hspace{0.17em}}\mathrm{cos}\left(\frac{2\pi }{3}\right)=-\frac{1}{2}$

$\frac{5\pi }{6}$

$\frac{7\pi }{4}$

$\frac{\pi }{4},$ Quadrant IV, $\text{\hspace{0.17em}}\text{sin}\left(\frac{7\pi }{4}\right)=-\frac{\sqrt{2}}{2},$ $\text{cos}\left(\frac{7\pi }{4}\right)=\frac{\sqrt{2}}{2}$

For the following exercises, find the requested value.

If $\text{\hspace{0.17em}}\text{cos}\left(t\right)=\frac{1}{7}\text{\hspace{0.17em}}$ and $\text{\hspace{0.17em}}t\text{\hspace{0.17em}}$ is in the 4 th quadrant, find $\text{\hspace{0.17em}}\text{sin}\left(t\right).$

If $\text{\hspace{0.17em}}\text{cos}\left(t\right)=\frac{2}{9}\text{\hspace{0.17em}}$ and $\text{\hspace{0.17em}}t\text{\hspace{0.17em}}$ is in the 1 st quadrant, find $\text{\hspace{0.17em}}\text{sin}\left(t\right).\text{\hspace{0.17em}}$

$\frac{\sqrt{77}}{9}$

If $\text{\hspace{0.17em}}\text{sin}\left(t\right)=\frac{3}{8}\text{\hspace{0.17em}}$ and $\text{\hspace{0.17em}}t\text{\hspace{0.17em}}$ is in the 2 nd quadrant, find $\text{\hspace{0.17em}}\text{cos}\left(t\right).$

If $\text{\hspace{0.17em}}\text{sin}\left(t\right)=-\frac{1}{4}\text{\hspace{0.17em}}$ and $\text{\hspace{0.17em}}t\text{\hspace{0.17em}}$ is in the 3 rd quadrant, find $\text{\hspace{0.17em}}\text{cos}\left(t\right).$

$-\frac{\sqrt{15}}{4}$

Find the coordinates of the point on a circle with radius 15 corresponding to an angle of $\text{\hspace{0.17em}}220°.$

Find the coordinates of the point on a circle with radius 20 corresponding to an angle of $\text{\hspace{0.17em}}120°.$

$\text{\hspace{0.17em}}\left(-10,10\sqrt{3}\right)\text{\hspace{0.17em}}$

Find the coordinates of the point on a circle with radius 8 corresponding to an angle of $\text{\hspace{0.17em}}\frac{7\pi }{4}.$

Find the coordinates of the point on a circle with radius 16 corresponding to an angle of $\text{\hspace{0.17em}}\frac{5\pi }{9}.$

$\text{\hspace{0.17em}}\left(–2.778,15.757\right)\text{\hspace{0.17em}}$

State the domain of the sine and cosine functions.

State the range of the sine and cosine functions.

$\text{\hspace{0.17em}}\text{\hspace{0.17em}}\left[–1,1\right]\text{\hspace{0.17em}}$

## Graphical

For the following exercises, use the given point on the unit circle to find the value of the sine and cosine of $\text{\hspace{0.17em}}t\text{\hspace{0.17em}.}$

$\mathrm{sin}t=\frac{1}{2},\mathrm{cos}t=-\frac{\sqrt{3}}{2}$

$\mathrm{sin}\text{\hspace{0.17em}}t=-\frac{\sqrt{2}}{2},\mathrm{cos}\text{\hspace{0.17em}}t=-\frac{\sqrt{2}}{2}$

$\mathrm{sin}\text{\hspace{0.17em}}t=\frac{\sqrt{3}}{2},\mathrm{cos}\text{\hspace{0.17em}}t=-\frac{1}{2}$

$\mathrm{sin}\text{\hspace{0.17em}}t=-\frac{\sqrt{2}}{2},\mathrm{cos}\text{\hspace{0.17em}}t=\frac{\sqrt{2}}{2}$

$\mathrm{sin}\text{\hspace{0.17em}}t=0,\mathrm{cos}\text{\hspace{0.17em}}t=-1$

$\mathrm{sin}\text{\hspace{0.17em}}t=-0.596,\mathrm{cos}\text{\hspace{0.17em}}t=0.803$

$\mathrm{sin}\text{\hspace{0.17em}}t=\frac{1}{2},\mathrm{cos}\text{\hspace{0.17em}}t=\frac{\sqrt{3}}{2}$

$\mathrm{sin}\text{\hspace{0.17em}}t=-\frac{1}{2},\mathrm{cos}\text{\hspace{0.17em}}t=\frac{\sqrt{3}}{2}$

$\mathrm{sin}\text{\hspace{0.17em}}t=0.761,\mathrm{cos}\text{\hspace{0.17em}}t=-0.649$

$\mathrm{sin}\text{\hspace{0.17em}}t=1,\mathrm{cos}\text{\hspace{0.17em}}t=0$

## Technology

For the following exercises, use a graphing calculator to evaluate.

$\mathrm{sin}\text{\hspace{0.17em}}\frac{5\pi }{9}$

$\mathrm{cos}\text{\hspace{0.17em}}\frac{5\pi }{9}$

−0.1736

$\mathrm{sin}\text{\hspace{0.17em}}\frac{\pi }{10}$

$\mathrm{cos}\text{\hspace{0.17em}}\frac{\pi }{10}$

0.9511

$\mathrm{sin}\text{\hspace{0.17em}}\frac{3\pi }{4}$

$\mathrm{cos}\text{\hspace{0.17em}}\frac{3\pi }{4}$

−0.7071

$\mathrm{sin}\text{\hspace{0.17em}}98°$

$\mathrm{cos}\text{\hspace{0.17em}}98°$

−0.1392

$\mathrm{cos}\text{\hspace{0.17em}}310°$

$\mathrm{sin}\text{\hspace{0.17em}}310°$

−0.7660

## Extensions

$\mathrm{sin}\left(\frac{11\pi }{3}\right)\mathrm{cos}\left(\frac{-5\pi }{6}\right)$

$\mathrm{sin}\left(\frac{3\pi }{4}\right)\mathrm{cos}\left(\frac{5\pi }{3}\right)$

$\frac{\sqrt{2}}{4}$

$\mathrm{sin}\left(-\frac{4\pi }{3}\right)\mathrm{cos}\left(\frac{\pi }{2}\right)$

$\mathrm{sin}\left(\frac{-9\pi }{4}\right)\mathrm{cos}\left(\frac{-\pi }{6}\right)$

$-\frac{\sqrt{6}}{4}$

$\mathrm{sin}\left(\frac{\pi }{6}\right)\mathrm{cos}\left(\frac{-\pi }{3}\right)$

$\mathrm{sin}\left(\frac{7\pi }{4}\right)\mathrm{cos}\left(\frac{-2\pi }{3}\right)$

$\frac{\sqrt{2}}{4}$

$\mathrm{cos}\left(\frac{5\pi }{6}\right)\mathrm{cos}\left(\frac{2\pi }{3}\right)$

$\mathrm{cos}\left(\frac{-\pi }{3}\right)\mathrm{cos}\left(\frac{\pi }{4}\right)$

$\frac{\sqrt{2}}{4}$

$\mathrm{sin}\left(\frac{-5\pi }{4}\right)\mathrm{sin}\left(\frac{11\pi }{6}\right)$

$\mathrm{sin}\left(\pi \right)\mathrm{sin}\left(\frac{\pi }{6}\right)$

0

## Real-world applications

For the following exercises, use this scenario: A child enters a carousel that takes one minute to revolve once around. The child enters at the point $\text{\hspace{0.17em}}\left(0,1\right),$ that is, on the due north position. Assume the carousel revolves counter clockwise.

What are the coordinates of the child after 45 seconds?

What are the coordinates of the child after 90 seconds?

$\left(0,–1\right)$

What is the coordinates of the child after 125 seconds?

When will the child have coordinates $\text{\hspace{0.17em}}\left(0.707,–0.707\right)\text{\hspace{0.17em}}$ if the ride lasts 6 minutes? (There are multiple answers.)

37.5 seconds, 97.5 seconds, 157.5 seconds, 217.5 seconds, 277.5 seconds, 337.5 seconds

When will the child have coordinates $\text{\hspace{0.17em}}\left(-0.866,-0.5\right)\text{\hspace{0.17em}}$ if the ride last 6 minutes?

how to understand calculus?
Hey I am new to precalculus, and wanted clarification please on what sine is as I am floored by the terms in this app? I don't mean to sound stupid but I have only completed up to college algebra.
I don't know if you are looking for a deeper answer or not, but the sine of an angle in a right triangle is the length of the opposite side to the angle in question divided by the length of the hypotenuse of said triangle.
Marco
can you give me sir tips to quickly understand precalculus. Im new too in that topic. Thanks
Jenica
if you remember sine, cosine, and tangent from geometry, all the relationships are the same but they use x y and r instead (x is adjacent, y is opposite, and r is hypotenuse).
Natalie
the standard equation of the ellipse that has vertices (0,-4)&(0,4) and foci (0, -15)&(0,15) it's standard equation is x^2 + y^2/16 =1 tell my why is it only x^2? why is there no a^2?
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This term is plural for a focus, it is used for conic sections. For more detail or other math questions. I recommend researching on "Khan academy" or watching "The Organic Chemistry Tutor" YouTube channel.
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meena
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I would like to add that they are used in AC signal analysis for one thing
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Good call Scott. Also radar signals I believe.
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