一 、
1、 ∫[1,2]xlnxdx,
用分部积分法,
设u=lnx, v’=x,
u’=1/x,v=x^2/2,
原式=[x^2lnx/2-(1/2)∫xdx] [1,2]
=( x^2lnx/2-x^2/4)[1,2]
=(4/2)(ln2)-4/4+1/4
=2ln2-3/4.
2、∫[0,1] x*e^2xdx,
和前题方法相同,
原式=[(1/2)x*e^2x-(1/2)∫e^2xdx] [0,1]
=[(1/2)x*e^2x –(1/4)e^2x] [0,1]
=e^2/2-e^2/4+1/4
=(e^2+1)/4.
3、∫[0,2] 2xdx/(x^2+4)
=∫[0,2] d(x^2+4)/(x^2+4)
=ln(x^2+4) [0,2]
=ln8-ln4
=3ln2-2ln2
=ln2.
4、∫[0,1]x^2*e^3xdx
仍用分部积分法,
原式=[x^2*e^3x/3-(2/3)∫x*e^3xdx] [0,1]
=[(1/3)x^2*e^(3x)-2x*e^(3x)/9+2e^(3x]/27] [0,1]
=[e^3/3-2e^3/9+2e^3/27-2/27]
=5e^3/27-2/27.
5、∫x*e^(-2x^2)dx
=(-1/4)∫e^(-2x^2)d(-2x^2)
=(-1/4)e^(-2x^2)+C.
二、f(x,y)=x^3y^2+x^2+2y,
f’x(x,y)[x=0,y=1]=3x^2y^2+2x=0,
f’y(x,y)[x=0,y=1]=2x^3y+2=2.
三、f’(x)=x^3+2x^2-3x+4
f(x)=∫f’(x)dx=x^4/4+2x^3/3-3x^2/2+4x+C.
四、f(x)=e^(3x)+e^(x^2+4x-5)
f’(x)=3*e^(3x)+e^( x^2+4x-5)*(2x+4)
=3e^(3x)+2(x+2)e^(x^2+4x-5).
五、计算x∈[0,2],由曲线y=2√x围绕Y轴的体积,
x=y^2/4,,当x=2时,y=2√2,
V=π∫[0,2√2] x^2dy
=(π/16)∫[0,2√2]y^4dy
=(π/16)(y^5/5)[0,2√2]
=8√2π/5。
六、
二重积分,D={( x,y)|0≤x≤2,0≤y≤x},
∫[D]∫(2x+3y)dxdy
=∫[0,2] dx∫[0,x](2x+3y)dy
=∫[0,2] dx (2xy+3y^2/2)[0,x]
=∫[0,2] (2x^2+3x^2/2)dx
=(2x^3/3+x^3/2)[0,2]
=7x^3/6[0,2]
=28/3.