2. Simple arrangement thinking.

3. Simple combinatorial thinking.

4. Simple combined thinking method is another way of expression.

Extended data:

In mathematics, radian is used instead of angle, because the divisibility of 360 is not important to mathematics, and radian is more convenient in mathematics. The relationship between angle and radian is: 2π radian = 360. Thus 1 ≈ 0.0 174533 radian, 1 radian ≈ 57.29578.

1) Angle to radian formula: radian = angle ÷ 180×π.

2) Formula for converting radian into angle: angle = radian×180÷π.