# Math Help - cot(x) and ln sin(x)

thanks

2. ## Re: cot(x) and ln sin(x)

Try $\int_{\frac{\pi}2}^xf(t)\,\mathrm dt \leqslant \int_{\frac{\pi}2}^x\cot t\,\mathrm dt \leqslant \int_{\frac{\pi}2}^xg(t)\,\mathrm dt$ for some functions $f(t),g(t).$

By the way, you stated the range of $x$ as $x\leq\frac{\pi}2\leq\pi$ but I think you mean $\frac\pi2\leq x<\pi.$

PS: $f(t)=\frac{\mathrm d}{\mathrm dt}\left[t\cot t\right]$ and $g(t)\equiv0.$

3. ## Re: cot(x) and ln sin(x)

I beg your pardon, the functions are negative in the given range so we need to do it this way:

Show that $0\leqslant -\cot t \leqslant -f(t)$ for $\frac{\pi}2\leqslant t<\pi$ where $f(t) = \frac{\mathrm d}{\mathrm dt}\left[t\cot t\right] = \cot t-t\csc^2t.$

Then integrate with respect to $t$ from $t=\frac{\pi}2$ to $t=x$ and multiply through by $-1.$

4. ## Re: cot(x) and ln sin(x)

Originally Posted by Sylvia104
Try $\int_{\frac{\pi}2}^xf(t)\,\mathrm dt \leqslant \int_{\frac{\pi}2}^x\cot t\,\mathrm dt \leqslant \int_{\frac{\pi}2}^xg(t)\,\mathrm dt$ for some functions $f(t),g(t).$

By the way, you stated the range of $x$ as $x\leq\frac{\pi}2\leq\pi$ but I think you mean $\frac\pi2\leq x<\pi.$

PS: $f(t)=\frac{\mathrm d}{\mathrm dt}\left[t\cot t\right]$ and $g(t)\equiv0.$

Sorry. yes . $\frac{\pi}{2}\leq x \leq \pi$

thanks

5. ## Re: cot(x) and ln sin(x)

thanks, but i can't understand. There another way?