令x=2sint 则dx=2costdt
当x=1时 t=π/6 当x=2时 t=π/2
原式=∫上限π/2,下限π/6 （2costdt）/2cost=∫上限π/2,下限π/6 dt=π/2-π/6=π/3
求定积分∫上限2,下限1 dx / (根号下4-x^2),
令x=2sint 则dx=2costdt
当x=1时 t=π/6 当x=2时 t=π/2
原式=∫上限π/2,下限π/6 （2costdt）/2cost=∫上限π/2,下限π/6 dt=π/2-π/6=π/3