高数问题 求人解答求人解答

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高数问题求人解答求人解答高数问题求人解答求人解答高数问题求人解答求人解答y'=∫dx/(1+x^2)设x=tant,则dx=(sect)^2*dt,t=arctanxy'=∫(sect

高数问题 求人解答求人解答
高数问题 求人解答

求人解答

高数问题 求人解答求人解答
y' = ∫dx/(1+x^2)
设 x = tant,则 dx = (sect)^2 *dt,t =arctanx
y'=∫(sect)^2 *dt/(sect)^2
  =∫dt
  = t + C1
  =arctanx + C1
y = ∫y' *dx
   = ∫(arctanx + C1)*dx
   = ∫arctanx *dx + C1*∫dx
   = x*arctanx - ∫x*dx/(1+x^2) + C1*x
   = x*arctanx - 1/2*∫d(1+x^2)/(1+x^2) + C1*x
   = x*arctanx - 1/2*ln(1+x^2) + C1*x + C
∫x*(x^2 + 1)^2 *dx
=1/2*∫(x^2+1)^2 *(2x*dx)
=1/2*∫(x^2+1)^2 *d(x^2 +1)
=1/2*1/3*(x^2+1)^3 + C
=1/6*(x^2+1)^3 + C

(5)y''=1/(1+x^2)令y'=dy/dx=p 则y''=dp/dx所以有dp/dx=1/(1+x^2)积分得 p=arctanx+C1即 dy/dx=arctanx+C1dy=(arctanx+C1)dx两边积分有 y=∫ (arctanx+C1)dx=∫ arctanxdx+C1x=xarctanx-∫ x/(1+x^2)dx+C1x=xarctanx-1/2∫ 1/(1+x^2)d(1+x^2)+C1x=xarctanx-1/2ln(1+x^2)+C1x+C2