How they say that it is the solution

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they said that the solution of

-dn=-\frac{1}{\tau}ndt\\

is

n=n_0e^{-\frac{t}{\tau}}



i got a totaly different answer

-dn=-\frac{1}{\tau}ndt\\
\int -dn=\int -\frac{1}{\tau}ndt\\
\int \frac{-dn}{n}=\int -\frac{1}{\tau}dt\\
-\ln{n}=-\frac{t}{\tau}\\
\ln{n^{-1}}=-\frac{t}{\tau}\\
e^{-\frac{t}{\tau}{={n^{-1}}
 
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Are you sure the negative sign in front of dn in the original equation is supposed to be there? You also forgot the constant of integration.
 
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...

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