V=π∫(0到1)(arccosy)²dy 设arccosy=t,那么y=cost V=π∫(π/2到0)t²dcost =π[t²cost|(π/2到0)-2∫(π/2到0)tcostdt] =-2π∫(π/2到0)tcostdt =-2π∫(π/2到0)tdsint =-2π[tsint|(π/2到0)-∫(π/2到0)sintdt] =π²+∫(π/2到0)sintdt =π²-cost|(π/2到0) =π²-1