由于f(x)为偶函数,故可设x>0,(x0积分一样).设x=(3/5)*tanα,则dx=(3/5)*(secα)^2dα 则原积分=9/5*∫√(1+(tanα)^2) * (secα)^2dα =9/5*∫(secα)^3dα 求I=∫(secα)^3dα,I=∫secα dtanα =secα*tanα-∫tan...
