令 x=asint, 则
∫ x^2dx/√(a^2-x^2) = ∫ a^2(sint)^2*acostdt/acost
= a^2 ∫ (sint)^2dt = (1/2)a^2 ∫ (1-cos2t)dt
= (1/2)a^2[t-(1/2)sin2t] + C
= (1/2)[a^2*arcsin(x/a) - x√(a^2-x^2)] + C
追问不明白∫ a^2(sint)^2dx/acost是怎么转化成∫ a^2(sint)^2*acostdt/acost,也就是dx如何变成acostdt,初学不太懂,希望详细说明,谢谢。
追答x=asint, 其微分 dx = acostdt