定积分上限1下限-1根号下1-x平方,别用几何意义求.急..
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定积分上限1下限-1根号下1-x平方,别用几何意义求.急..
定积分上限1下限-1根号下1-x平方,别用几何意义求.急..
定积分上限1下限-1根号下1-x平方,别用几何意义求.急..
解析:如果不用几何意义求就用换元法!
令x=sint,则当x=-1时,t=-π/2,x=1时,t=π/2,所以原式=
∫(-π/2,π/2)costdsint
=∫(-π/2,π/2)cos²tdt
=1/2∫(-π/2,π/2)(1+cos2t)dt
=1/2(t+1/2sin2t)|(-π/2,π/2)
=π/4-(-π/4)
=π/2.
令x = sinz,dx = cosz dz
当x = - 1、z = - π/2
当x = 1、z = π/2
∫(- 1→1) √(1 - x^2) dx
= ∫(- π/2→π/2) √(1 - (sinz)^2) * (cosz dz)
= 2∫(0→π/2) |cosz| * cosz dz,由于偶函数,关于x = 0对称,变为原被积函数的两倍
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令x = sinz,dx = cosz dz
当x = - 1、z = - π/2
当x = 1、z = π/2
∫(- 1→1) √(1 - x^2) dx
= ∫(- π/2→π/2) √(1 - (sinz)^2) * (cosz dz)
= 2∫(0→π/2) |cosz| * cosz dz,由于偶函数,关于x = 0对称,变为原被积函数的两倍
= 2(0→π/2) (cosz)^2 dz
= 2∫(0→π/2) (1 + cos(2z))/2 dz
= [z + (1/2)cos(2z)] |(0→π/2)
= (π/2 + 0) - (0)
= π/2
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