Tính các nguyên hàm sau đây: ∫ x + ln x x 2 d x
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`a)TXĐ:R\\{1;1/3}`
`y'=[-4(6x-4)]/[(3x^2-4x+1)^5]`
`b)TXĐ:R`
`y'=2x. 3^[x^2-1] ln 3-e^[-x+1]`
`c)TXĐ: (4;+oo)`
`y'=[2x-4]/[x^2-4x]+2/[(2x-1).ln 3]`
`d)TXĐ:(0;+oo)`
`y'=ln x+2/[(x+1)^2].2^[[x-1]/[x+1]].ln 2`
`e)TXĐ:(-oo;-1)uu(1;+oo)`
`y'=-7x^[-8]-[2x]/[x^2-1]`
Lời giải:
a.
$y'=-4(3x^2-4x+1)^{-5}(3x^2-4x+1)'$
$=-4(3x^2-4x+1)^{-5}(6x-4)$
$=-8(3x-2)(3x^2-4x+1)^{-5}$
b.
$y'=(3^{x^2-1})'+(e^{-x+1})'$
$=(x^2-1)'3^{x^2-1}\ln 3 + (-x+1)'e^{-x+1}$
$=2x.3^{x^2-1}.\ln 3 -e^{-x+1}$
c.
$y'=\frac{(x^2-4x)'}{x^2-4x}+\frac{(2x-1)'}{(2x-1)\ln 3}$
$=\frac{2x-4}{x^2-4x}+\frac{2}{(2x-1)\ln 3}$
d.
\(y'=(x\ln x)'+(2^{\frac{x-1}{x+1}})'=x(\ln x)'+x'\ln x+(\frac{x-1}{x+1})'.2^{\frac{x-1}{x+1}}\ln 2\)
\(=x.\frac{1}{x}+\ln x+\frac{2}{(x+1)^2}.2^{\frac{x-1}{x+1}}\ln 2\\ =1+\ln x+\frac{2^{\frac{2x}{x+1}}\ln 2}{(x+1)^2}\)
e.
\(y'=-7x^{-8}-\frac{(x^2-1)'}{x^2-1}=-7x^{-8}-\frac{2x}{x^2-1}\)
g: \(y=ln\left(x^2+x+1\right)\)
=>\(y'=\dfrac{\left(x^2+x+1\right)'}{x^2+x+1}=\dfrac{2x+1}{x^2+x+1}\)
l: \(y=\dfrac{lnx}{x+1}\)
=>\(y'=\dfrac{\left(lnx\right)'\cdot\left(x+1\right)-\left(x+1\right)'\left(lnx\right)}{\left(x+1\right)^2}\)
=>\(y'=\dfrac{\dfrac{1}{x}\left(x+1\right)-lnx}{\left(x+1\right)^2}\)
\(\Leftrightarrow y'=\dfrac{\dfrac{\left(x+1\right)}{x}-lnx}{\left(x+1\right)^2}\)
1.
\(y'=\left(\dfrac{x}{lnx}\right)'.3^{\dfrac{x}{lnx}}.ln3=\dfrac{lnx-1}{ln^2x}.3^{\dfrac{x}{lnx}}.ln3\)
2.
\(y'=\left(tanx\right)'.tanx+\left(tanx\right)'.\dfrac{1}{tanx}=\dfrac{tanx}{cos^2x}+\dfrac{1}{tanx.cos^2x}\)
3.
\(y=\left(ln2x\right)^{\dfrac{2}{3}}\Rightarrow y'=\left(ln2x\right)'.\dfrac{2}{3}.\left(ln2x\right)^{-\dfrac{1}{3}}=\dfrac{1}{3x\sqrt[3]{ln2x}}\)
\(\int\left(3x^2-2x-4\right)dx=x^3-x^2-4x+C\)
\(\int\left(sin3x-cos4x\right)dx=-\dfrac{1}{3}cos3x-\dfrac{1}{4}sin4x+C\)
\(\int\left(e^{-3x}-4^x\right)dx=-\dfrac{1}{3}e^{-3x}-\dfrac{4^x}{ln4}+C\)
d. \(I=\int lnxdx\)
Đặt \(\left\{{}\begin{matrix}u=lnx\\dv=dx\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}du=\dfrac{dx}{x}\\v=x\end{matrix}\right.\)
\(\Rightarrow u=x.lnx-\int dx=x.lnx-x+C\)
e. Đặt \(\left\{{}\begin{matrix}u=x\\dv=e^xdx\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}du=dx\\v=e^x\end{matrix}\right.\)
\(\Rightarrow I=x.e^x-\int e^xdx=x.e^x-e^x+C\)
f.
Đặt \(\left\{{}\begin{matrix}u=x+1\\dv=sinxdx\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}du=dx\\v=-cosx\end{matrix}\right.\)
\(\Rightarrow I=-\left(x+1\right)cosx+\int cosxdx=-\left(x+1\right)cosx+sinx+C\)
g.
Đặt \(\left\{{}\begin{matrix}u=lnx\\dv=xdx\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}du=\dfrac{dx}{x}\\v=\dfrac{1}{2}x^2\end{matrix}\right.\)
\(\Rightarrow I=\dfrac{1}{2}x^2.lnx-\dfrac{1}{2}\int xdx=\dfrac{1}{2}x^2.lnx-\dfrac{1}{4}x^2+C\)
\(\int xln\left(x+1\right)dx\)
\(\left\{{}\begin{matrix}u=ln\left(x+1\right)\\dv=xdx\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}du=\dfrac{1}{x+1}dx\\v=\dfrac{x^2}{2}\end{matrix}\right.\)
\(\Rightarrow\int xln\left(x+1\right)dx=\dfrac{x^2}{2}.ln\left(x+1\right)-\int\dfrac{x^2}{2}.\dfrac{1}{x+1}dx=\dfrac{x^2}{2}.ln\left(x+1\right)-\dfrac{1}{2}\int\dfrac{x^2}{x+1}dx\)
Xet \(\int\dfrac{x^2}{x+1}dx=\int\dfrac{\left(x+1\right)\left(x-1\right)}{x+1}dx+\int\dfrac{1}{x+1}dx\)
\(=\int\left(x-1\right)dx+\int\dfrac{1}{x+1}dx\)
\(=\dfrac{x^2}{2}-x+ln\left(x+1\right)\)
\(\Rightarrow\int xln\left(x+1\right)dx=\dfrac{x^2}{2}.ln\left(x+1\right)-\dfrac{1}{2}\left(\dfrac{x^2}{2}-x+ln\left(x+1\right)\right)\)
\(a,y'=8x^3-9x^2+10x\\ \Rightarrow y''=24x^2-18x+10\\ b,y'=\dfrac{2}{\left(3-x\right)^2}\\ \Rightarrow y''=\dfrac{4}{\left(3-x\right)^3}\)
\(c,y'=2cos2xcosx-sin2xsinx\\ \Rightarrow y''=-5sin\left(2x\right)cos\left(x\right)-4cos\left(2x\right)sin\left(x\right)\\ d,y'=-2e^{-2x+3}\\ \Rightarrow y''=4e^{-2x+3}\)
x 4 4 + x 3 3 ln x - 1 3 + C
Hướng dẫn: Đặt u = x + lnx; dv = x 2 dx