举例说明如何运用第一类换元法（凑微分法）求不定积分

(There is not a Chinese input program on my machine, sorry!)According to the formula ∫dx=x+C
For example
1.∫sin xdx=∫-dcosx=-cosx+C
2.∫1/x dx=∫dlnx=ln|x|+C
3.∫x^4dx=∫x^5/5dx=x^5dx+C
4.∫tanx dx=∫sinxdx/cosx=∫-dcosx/cosx
Define u=cosx ∫tan x dx=∫-du/u=-ln|u| +C
=-ln|cosx|+C

就是把一个复杂点的元素换成一个简间的