∫(0,3/4) 1/(x+1)√(x²+1)dx 令：x=tant=∫(0,3/4) tantsect/(tant+1)sectdt= 3/4 - ∫(0,3/4) 1/(tant+1)sectdt=3/4 - 1/2∫(0,3/4) [（cost+sint）+（sint-cost）]/(sint+cost)dt
