First spend 45 degrees with the angle of a 45-degree triangle, and then draw a 30-degree angle with one side of the angle of a 30-degree triangle aligned with the other side of the 45-degree angle. Their difference is 15 degrees.

The sine value of 15 degree angle is (√6-√2)/4 and the cosine value is (√6+√2)/4.

sin 15 du = sin(60-45)= sin 60 cos 45-cos 60 sin 45

=√6/4-√2/4=(√6-√2)/4

Cos15 = √ (1-sin15 squared) =(√6+√2)/4.

Extended data:

Related theorem:

Property theorem: A point on the bisector of an angle is equal to the distance between the two sides of the angle.

Decision theorem: the point to which both sides of an angle are equidistant is on the bisector of this angle.

The point on the bisector of an angle is equal to the distance on both sides of the angle.

If a point in an angle is equal to the distance between two sides of the angle, the point is on the bisector of the angle.

Baidu encyclopedia-jiao