高数题求答
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高数题求答
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1、lim (x^2-2x3)/sin(x+1) (x-->-1)
=lim (x+1)*(x-3)/sin(x+1) (x-->-1)
=lim (x+1)/sin(x+1)* lim(x-3) (x-->-1)
=-4
2、∫ 1/(x√(1+lnx)) dx
=∫ 1/√(1+lnx) d(1+lnx)
=∫ (1+lnx)^(-1/2) d(1+lnx)
= 2 (1+lnx)^(1/2) + C
= 2 √(1+lnx) + C
3、∫ ln(x)/√x dx (x=1,e)
=∫ 2ln(x) d√x (x=1,e)
=∫ 2ln(t^2) dt (t=1,√e)
=∫ 4ln(t) dt (t=1,√e)
=-4t + 4t lnt (t=1,√e)
=4-2√e
4、dy=-3cos^2 (x)sin(x) -2x
5、设圆柱体底半径为r,高为h,有:h=√(L^2-r^2)
体积V(r)=πr^2h=πr^2√(L^2-r^2)
用高数的方法求V(r)的极值,令d(V)/d(r)=0
得到:2r(L^2-r^2)^(1/2)-r^3(L^2-r^2)^(-1/2)=0
解得:r=0或r=√6/3 L
后者符合题意.
=lim (x+1)*(x-3)/sin(x+1) (x-->-1)
=lim (x+1)/sin(x+1)* lim(x-3) (x-->-1)
=-4
2、∫ 1/(x√(1+lnx)) dx
=∫ 1/√(1+lnx) d(1+lnx)
=∫ (1+lnx)^(-1/2) d(1+lnx)
= 2 (1+lnx)^(1/2) + C
= 2 √(1+lnx) + C
3、∫ ln(x)/√x dx (x=1,e)
=∫ 2ln(x) d√x (x=1,e)
=∫ 2ln(t^2) dt (t=1,√e)
=∫ 4ln(t) dt (t=1,√e)
=-4t + 4t lnt (t=1,√e)
=4-2√e
4、dy=-3cos^2 (x)sin(x) -2x
5、设圆柱体底半径为r,高为h,有:h=√(L^2-r^2)
体积V(r)=πr^2h=πr^2√(L^2-r^2)
用高数的方法求V(r)的极值,令d(V)/d(r)=0
得到:2r(L^2-r^2)^(1/2)-r^3(L^2-r^2)^(-1/2)=0
解得:r=0或r=√6/3 L
后者符合题意.