Integrating ln(t+1) from 0 to e^2x?

Enujybab
Messages
1
Reaction score
0

Homework Statement


How would I begin to integrate ln(t+1) from 0 to e^2x?


Homework Equations


d/dx[log base a of u]=1/(lna)u du/dx

Can the original equation be manipulated to use this derivative?


The Attempt at a Solution


Not sure where to start.
 
Physics news on Phys.org
It's the sort of problem where you could actually guess the antiderivative, but if you can't, integrate by parts.
 
It's an integration by part question. First, use a substitution to get it to one variable instead of a polynomial in the logarithm.
w=t+1
dw=dt
Substitute (I'm going to revert the limits in the end to the original variable, so you know):
Integrate of ln(w)dw
Let:
u=ln(w) and dv=dw
du=(1/w)*dw and v=w

w*ln(w)-Int(w*(1/w)*dw)
w*ln(w)-Int(dw)
w*ln(w)-w
(t+1)*[ln(t+1)-1]
now evaluate at your endpoints:
{(e^2x+1)*[ln(e^2x+1)-1]}+{1}
You can probably simplify this some more, but there it is.
 
Prove $$\int\limits_0^{\sqrt2/4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx = \frac{\pi^2}{8}.$$ Let $$I = \int\limits_0^{\sqrt 2 / 4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx. \tag{1}$$ The representation integral of ##\arcsin## is $$\arcsin u = \int\limits_{0}^{1} \frac{\mathrm dt}{\sqrt{1-t^2}}, \qquad 0 \leqslant u \leqslant 1.$$ Plugging identity above into ##(1)## with ##u...
Back
Top