Mathematics
Grade 12
15 min
Convert between radians and degrees
Convert between radians and degrees
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1
Introduction & Learning Objectives
Learning Objectives
Define a radian in terms of a circle's radius and arc length.
Recall and state the fundamental relationship between degrees and radians (180° = π radians).
Accurately convert angle measures from degrees to radians, expressing answers in terms of π.
Precisely convert angle measures from radians to degrees.
Use a calculator to find decimal approximations for conversions between the two units.
Identify the degree and radian measures of key angles on the unit circle (e.g., 30°, 45°, 60°, 90°).
Apply angle conversion to solve problems in contexts like angular velocity.
Ever wondered why the derivatives of sin(x) and cos(x) only work when x is in radians? 🤔 Let's unlock the fundamental reason by mastering the language of circles!
This tutorial wil...
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Key Concepts & Vocabulary
TermDefinitionExample
Degree (°)A unit of angular measure, defined such that a full rotation of a circle is 360 degrees. It is a historical unit derived from Babylonian astronomy.A right angle is 90°, a straight line is 180°, and a full circle is 360°.
Radian (rad)The measure of a central angle of a circle that intercepts an arc equal in length to the radius of that circle. It is a more 'natural' unit for mathematics as it is directly derived from the circle's own properties.If a circle has a radius of 5 cm, a 1 radian angle cuts off an arc that is also 5 cm long.
Unit CircleA circle with a radius of 1 unit, centered at the origin of the Cartesian plane. Its circumference is 2π units.On the unit circle, an angle of π/2 radians corresponds to the point (0, 1), which is 90° f...
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Core Formulas
Degrees to Radians Conversion
\text{Radians} = \text{Degrees} \times \frac{\pi}{180^\circ}
To convert an angle from degrees to radians, multiply the degree measure by the conversion factor π/180°. This is used when you are given degrees and need to find radians, especially for calculus operations.
Radians to Degrees Conversion
\text{Degrees} = \text{Radians} \times \frac{180^\circ}{\pi}
To convert an angle from radians to degrees, multiply the radian measure by the conversion factor 180°/π. This is useful for visualizing the size of an angle given in radians.
Fundamental Relationship
\pi \text{ radians} = 180^\circ
This core identity is the basis for both conversion formulas. It states that a half-circle rotation measures π in radians and 180 in degrees. Remembering...
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Challenging
The formula for the area of a circular sector, A = (1/2)r²θ, is valid only when θ is in radians. What is the area of a sector with a central angle of 72° in a circle with a radius of 10 units?
A.40π units²
B.20π units²
C.360 units²
D.720 units²
Challenging
The sum of the numerical value of an angle's measure in degrees and its measure in radians is `180 + π`. What is the angle's measure in degrees?
A.π°
B.90°
C.180°
D.360°
Challenging
The calculus limit `lim (x->0) sin(x)/x = 1` holds for x in radians. The equivalent for x in degrees is `lim (x->0) sin(x°)/x° = π/180`. Using this information, what is the value of `lim (x->0) sin(4x°)/x°`?
A.4
B.4π/180
C.1
D.π/45
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