We're used to measuring angles in degrees. However, angles can also be measured in radians (sometimes written as ""). One radian is the angle formed at the center of a circle by an arc whose length is equal to the radius of the circle.
To find the number of radians in a circle, we divide the circumference of the circle by the length of a radius. We always get the same result:
So, we have that
is equivalent to radians, and
is equivalent to radians.
As a consequence,
to convert degrees to radians, we must multiply by and
to convert radians to degrees, multiply by
An angle of is equal to how many radians?
To convert the measure of an angle in degrees to an equivalent measure in radians, we multiply the measure in degrees by This gives
Therefore, is equivalent to radians.
Notice that when we divide by we can drop the degree symbol.
An angle of $40^\circ$ is equal to how many radians?
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a
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$\dfrac {7\pi} {2}$ |
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b
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$\dfrac {\pi} {7}$ |
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c
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$\dfrac {5\pi} {4}$ |
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d
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$\dfrac {5\pi} {7}$ |
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e
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$\dfrac {2\pi} {9}$ |
One-half of a full rotation is equal to how many radians?
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a
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$2\pi$ radians |
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b
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$\pi$ radians |
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c
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$4\pi$ radians |
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d
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$\dfrac {\pi} 4$ radians |
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e
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$\dfrac {\pi} 2$ radians |
What is the angle of radians in degrees?
To convert the measure of an angle in radians to an equivalent measure in degrees, we multiply the measure in radians by This gives
Therefore, is equivalent to
An angle of $\dfrac{\pi}{8}$ radians is equal to
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a
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b
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c
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d
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e
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What is the angle of $2 \pi $ radians in degrees?
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a
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$90^\circ$ |
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b
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$180^\circ$ |
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c
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$160^\circ$ |
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d
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$150^\circ$ |
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e
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$360^\circ$ |
What is radians in degrees to the nearest degree?
To convert the measure of an angle in radians to an equivalent measure in degrees, we multiply the measure in radians by
Evaluating this using a calculator, we get
rounded to decimal places. Therefore, radians is equal to to the nearest degree.
What is $0.957$ radians in degrees to the nearest degree?
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a
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$55^\circ$ |
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b
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$102^\circ$ |
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c
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$86^\circ$ |
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d
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$47^\circ$ |
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e
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$36^\circ$ |
Rounded to the nearest degree, an angle of $\dfrac{6\pi}{13}$ radians is equal to
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a
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b
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c
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d
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e
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Rounding to one decimal place, what is measured in radians?
To convert the measure of an angle in degrees to an equivalent measure in radians, we multiply the measure in degrees by
Evaluating this using a calculator, we get
rounded to decimal places.
Therefore, the angle is equal to radians rounded to one decimal place.
Rounded to one decimal place, $99^\circ$ is equal to
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a
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b
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c
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d
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e
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Rounded to one decimal place, what is $48.6^\circ$ measured in radians?
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a
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$0.8$ |
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b
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$0.7$ |
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c
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$0.4$ |
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d
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$0.3$ |
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e
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$0.5$ |
The table below summarizes the values of some special angles in degrees and radians.
| Degrees | ||||||||
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| Radians | ||||||||
| Degrees | ||||||||
| Radians |
Radians might seem a weird way of measuring angles now, but as you learn about trigonometry, you'll come to realize that they can be very useful and convenient.