Isn't sin0 equal to 0? Why is the final result here 1?  

Isn't sin0 equal to 0? Why is the final result here 1?  

Yes, when sin0 is 0, but the problem is that sinu can be approximately regarded as sin0 when u tends to a very small number, but it is not sin0, it is a very small number, very small. The growth rate of sinu and u when u tends to 0 is almost the same, so the ratio of the two is 1

The reason why cos90 equals 0 and the reason why sin0
How to solve the problem of unit circle on the first floor

The problem of trigonometric function is usually solved in the unit circle, the radius is 1, other as long as the right side is compared with the right side, in the unit circle, the hypotenuse of triangle is fixed length is 1, the angle can change at will, and the calculation rule of trigonometric function is unchanged, that is, cos is the adjacent side than the upper hypotenuse, sin is the opposite side than the upper hypotenuse, t