如何用换元法算根号根号(1-X平方) X属于0到1的定积分设x=sint,dx=costdt,x=0,t=0,x=1,t=π/2,∫[0,1]√(1-x^2)dx=∫[0,π/2]cost*costdt (根号怎么约去的 ) =∫[0,π/2](cost)^2dt=(1/2)∫[0,π/2](1+cos2t)dt=[0,π/2](t/2)+(1/4

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如何用换元法算根号根号(1-X平方) X属于0到1的定积分设x=sint,dx=costdt,x=0,t=0,x=1,t=π/2,∫[0,1]√(1-x^2)dx=∫[0,π/2]cost*costdt (根号怎么约去的 ) =∫[0,π/2](cost)^2dt=(1/2)∫[0,π/2](1+cos2t)dt=[0,π/2](t/2)+(1/4
如何用换元法算根号根号(1-X平方) X属于0到1的定积分
设x=sint,dx=costdt,x=0,t=0,x=1,t=π/2,
∫[0,1]√(1-x^2)dx=∫[0,π/2]cost*costdt (根号怎么约去的 ) =∫[0,π/2](cost)^2dt=(1/2)∫[0,π/2](1+cos2t)dt
=[0,π/2](t/2)+(1/4)[0,π/2]sin2t=π/4.补充:(cost)'=-sint.

如何用换元法算根号根号(1-X平方) X属于0到1的定积分设x=sint,dx=costdt,x=0,t=0,x=1,t=π/2,∫[0,1]√(1-x^2)dx=∫[0,π/2]cost*costdt (根号怎么约去的 ) =∫[0,π/2](cost)^2dt=(1/2)∫[0,π/2](1+cos2t)dt=[0,π/2](t/2)+(1/4
√(1-x^2)=√(1-sin^2t)=√cos^2t=cost

令√(1-x^2)=cost,则(1-x^2)=cost^2可推得x=sint,dx=costdt。可得∫[0,1]√(1-x^2)dx=∫[0,π/2]cost*costdt