Trigonometry · Radians and the unit circle

How to Convert Degrees to Radians

Problem

135∘135^\circ

Answer

3π4\frac{3\pi}{4}

Radians measure angles with the radius as the unit. A full turn is 2pi radians, which is the same as 360 degrees.

Step-by-step solution

  1. Multiply the degrees by pi/180.

    135∘×π180∘135^\circ \times \frac{\pi}{180^\circ}

    Why: A full turn is 360 degrees or 2pi radians, so the factor between them is pi/180.

  2. Multiply the numbers.

    135π180\frac{135\pi}{180}

    Why: The degree symbols cancel.

  3. Simplify the fraction by 45.

    135π180=3π4\frac{135\pi}{180} = \frac{3\pi}{4}

    Why: 135 divided by 45 is 3, and 180 divided by 45 is 4.

Common mistakes

  • Multiplying by 180/pi instead of pi/180.
  • Leaving the degree symbol in the answer. Radians have no unit symbol.
  • Simplifying the pi away. Pi stays in the answer.

Practice problems

Use the same method. Work each problem on paper, then open the answer to check.

  1. 90∘90^\circ

    Show answer

    π2\frac{\pi}{2}

  2. 180∘180^\circ

    Show answer

    π\pi

  3. 60∘60^\circ

    Show answer

    π3\frac{\pi}{3}

  4. 45∘45^\circ

    Show answer

    π4\frac{\pi}{4}

  5. 270∘270^\circ

    Show answer

    3π2\frac{3\pi}{2}