đặt t = lnx

tôi ko biết \(\varepsilon\) trong bài là gì, tuy nhiên nếu nó là số bất kì thì xét 2 TH sau để biết đk t

TH1: \(\varepsilon\in\left(0;1\right)\)

TH2: \(\varepsilon>1\)

Đặt \(t=x^2+5\rightarrow\begin{cases}dt=2xdx,x=0\rightarrow t=5,x=3\rightarrow t=14\\f\left(x\right)dx=x\ln\left(x^2+5\right)dx=\frac{1}{2}\ln tdt\end{cases}\)

Do đó : \(I=\frac{1}{2}\int\limits^{14}_5\ln tdt=\frac{1}{2}\left(t\ln t\right)|^{14}_5=\frac{14\ln14-5\ln5-11}{2}\)

\(I=\frac{1}{4}\int\limits^e_1\frac{4\ln^2x-1+1}{x\left(1+2\ln x\right)}dx=\frac{1}{4}\int\limits^e_1\frac{\left(2\ln x-1\right)dx}{x}+\frac{1}{4}\int\limits^e_1\frac{dx}{x\cdot\left(1+2\ln x\right)}\)

  \(=\frac{1}{8}\int\limits^e_1\left(2\ln x-1\right)d\left(2\ln x-1\right)+\frac{1}{8}\int\limits^e_1\frac{d\left(2\ln x+1\right)}{\left(1+2\ln x\right)}\)

   \(=\left(\frac{1}{16}\left(2\ln x-1\right)^2\right)|^e_1+\frac{1}{8}\ln\left|\left(1+2\ln x\right)\right||^e_1\)

    \(=\frac{1}{8}\ln3\)

Ta có \(I=\int\limits^{\frac{\pi}{3}}_{\frac{\pi}{4}}\frac{\ln2.\ln\left(2\tan x\right)}{\sin2x.\ln\left(2\tan x\right)}dx=\ln2\int\limits^{\frac{\pi}{3}}_{\frac{\pi}{4}}\frac{dx}{\sin2x.\ln\left(2\tan x\right)}+\int\limits^{\frac{\pi}{3}}_{\frac{\pi}{4}}\frac{dx}{\sin2x}\)

Tính \(\ln2\int\limits^{\frac{\pi}{3}}_{\frac{\pi}{4}}\frac{dx}{\sin2x.\ln\left(2\tan x\right)}=\frac{\ln2}{2}\int\limits^{\frac{\pi}{3}}_{\frac{\pi}{4}}\frac{d\left[\ln\left(2\tan x\right)\right]}{\ln2\left(2\tan x\right)}=\frac{\ln2}{2}\left[\ln\left(\ln\left(2\tan x\right)\right)\right]|^{\frac{\pi}{3}}_{\frac{\pi}{4}}=\frac{\ln2}{2}.\ln\left(\frac{\ln2\sqrt{3}}{\ln2}\right)\)

Tính \(\int\limits^{\frac{\pi}{3}}_{\frac{\pi}{4}}\frac{dx}{\sin2x}=\frac{1}{2}\ln\left(\tan x\right)|^{\frac{\pi}{3}}_{\frac{\pi}{4}}=\frac{1}{2}\ln\sqrt{3}\)

Vậy \(I=\frac{\ln2}{2}\ln\left(\frac{\ln2\sqrt{3}}{\ln2}\right)+\frac{1}{2}\ln\sqrt{3}\)

Đáp án đúng : B

a) \(\int\dfrac{2dx}{x^2-5x}=\int\left(\dfrac{-2}{5x}+\dfrac{2}{5\left(x-5\right)}\right)dx=-\dfrac{2}{5}ln\left|x\right|+\dfrac{2}{5}ln\left|x-5\right|+C\)

\(\Rightarrow A=-\dfrac{2}{5};B=\dfrac{2}{5}\Rightarrow2A-3B=-2\)

b) \(\int\dfrac{x^3-1}{x+1}dx=\int\dfrac{x^3+1-2}{x+1}dx=\int\left(x^2-x+1-\dfrac{2}{x+1}\right)dx=\dfrac{1}{3}x^3-\dfrac{1}{2}x^2+x-2ln\left|x+1\right|+C\)

\(\Rightarrow A=\dfrac{1}{3};B=\dfrac{1}{2};E=-2\Rightarrow A-B+E=-\dfrac{13}{6}\)

Ta có : \(I=\int\limits^2_12x^3dx+\int\limits^2_1\ln xdx\)

Đặt \(I_1=\int\limits^2_12x^3dx\) và \(I_2=\int\limits^2_1\ln xdx\)

Ta có : 

\(I_1=\frac{1}{2}x^4|^2_1=\frac{15}{2}\)

\(I_2=x.\ln x|^2_1-\int_1xd^2\left(\ln x\right)=2\ln2-x|^2_1=2\ln2-1\)

Vậy \(I=I_1+I_2=\frac{13}{2}+2\ln2\)