In an angle, any number without a degree sign is radian. Especially remember the pie in the arc system. Pie chart =3. 14 radian = 180 degrees. In this way, you have solved all the problems.

1. Prove the sector area formula S = 1/2 LR by arc system, where L is the arc length of the sector and R is the radius of the circle. (The area of the circle is R*R, where r is the arc length.)

2. Why don't you understand the answer to calculate tan 1.5?

57.30 degrees multiplied by 1.5=89.95 degrees =85 degrees and 57 minutes (where 1.5 has no scale, it is radian, which can be expressed by a round cake,1.5 =1.5/3.1.

3. Turn -3 15 degrees into an angle of 0 to 2 pie plus the form of 2k pie.

I don't understand why the answer is -3 15 degrees =45 degrees -360 degrees =4 points -2 schools. (Change the pie chart to 180 degrees to get the result.)