This is the most primitive set of equations, its content is not very clear, the left side of the equation looks too troublesome.
Therefore it still needs some modification.
As for where the idea for modification comes from?
Of course, it is sinθ.
Xu Yun picked up a pen and drew a right triangle on the paper.
As everyone knows.
The sine value sinθ equals the opposite side c divided by the hypotenuse a, the tangent value tanθ equals the opposite side c divided by the adjacent side b.
Xu Yun drew another right triangle with a very small angle, estimating only a few degrees:
"But once the angle θ is very, very small, then the adjacent side b and the hypotenuse a almost coincide."
"At this time, we can approximately assume that a and b are equal, that is, a≈b."
Subsequently, he wrote on the paper:
[Thus c/b≈c/a, that is, tanθ≈sinθ.]
[The previous formula can be written as F= T·tan(θ+Δθ) - T·tanθ = μ·Δxa∂²f/∂t².]
"One moment."
