The function y=f(x), and its differential formula is dy=f'(x)dx★
Take y=sinx as an example, and dy=cosxdx, that is, dsinx=cosxdx▲
Interpret the meaning of the formula dy = f ′ (x) dx★ from two directions:
① Direction from left to right:
Formula★ From left to right is to distinguish:
For example, y=sinx, and differential dy=cosxdx from left to right.
② Direction from right to left:
Formula★ From right to left is differential:
For example, make cosxdx into differential form dsinx, see ▲.
To put it bluntly, it is to replace cosx in cosxdx with sinx and gather it to the right of the difference symbol D to become dsinx.
That is to say,
Put < cosx > in *