求广义积分∫(1/2~3/2)(√(x-x²)的绝对值)dx

1个回答

  • ∫[1/2,3/2]√|(x-x^2)|dx

    =∫[1/2,3/2]√|(x-1/2)^2-1/4|dx

    =∫[1/2,1] √[1/4-(x-1/2)^2]dx +∫[1,3/2]√[(x-1/2)^2-1/4]dx

    =(1/2)x√(x-x^2)-(1/2)√(x-x^2)+(1/4)arcsin(2x-1) |[1/2,1]

    +(1/2)x√(x^2-x)-(1/2)√(x^2-x)-(1/4)ln|√(x^2-x)+(x-1/2)| |[1,3/2]

    ∫√(x-x^2)dx

    =x√(x-x^2)+∫x(x-1/2)dx/√(x-x^2)

    =x√(x-x^2)-∫√(x-x^2)dx+∫(x/2)dx/√(x-x^2)

    =x√(x-x^2)-∫√(x-x^2)dx+(-1/2)∫d(x-x^2)/√(x-x^2)+(1/2)∫dx/√(x-x^2)

    =x√(x-x^2)-∫√(x-x^2)dx-√(x-x^2)+(1/2)∫d(2x-1)/√(1-(2x-1)^2)

    =x√(x-x^2)-√(x-x^2)+(1/2)arcsin(2x-1)-∫√(x-x^2)dx

    ∫√(x-x^2)dx=(1/2)x√(x-x^2)-(1/2)√(x-x^2)+(1/4)arcsin(2x-1)

    ∫√(x^2-x)dx

    =x√(x^2-x)-∫√(x^2-x)dx-(1/2)∫xdx/√(x^2-x)

    =x√(x^2-x)-∫√(x^2-x)dx-√(x^2-x)-(1/2)∫dx/√(x^2-x)

    =x√(x^2-x)-∫√(x^2-x)dx-√(x^2-x)-(1/2)∫d(2x-1)/√[(2x-1)^2-1]

    2x-1=secu ∫d(2x-1)/√[(2x-1)^2-1]=∫secudu=ln|secu+tanu|=ln|√(x^2-x)+(x-1/2)|

    ∫√(x^2-x)dx=(1/2)x√(x^2-x)-(1/2)√(x^2-x)-(1/4)ln|√(x^2-x)+(x-1/2)|