The sine of 20 degrees is 0.34. The sine is calculated by using the Pythagorean Theorem to find the length of the side of a right triangle opposite the 20 degree angle and dividing that length by the length of the hypotenuse.
The formula for the sine of 20 degrees is written as the square root of 0.46 divided by two. The square root of 0.46 is 0.68, which becomes 0.34 when divided by two. The cosine of a 20 degree angle is 0.93, and the tangent is 0.36. Many calculators contain a key for determining the sine function of an angle.