# arcsec proplem pls

• Sep 24th 2009, 02:08 PM
kevintrung
arcsec proplem pls
Evaluate arcsec sec -9pie/7

pleas explain the steps thanks
• Sep 24th 2009, 03:21 PM
skeeter
Quote:

Originally Posted by kevintrung
Evaluate arcsec sec -9pie/7

pleas explain the steps thanks

you need to know that the range of the inverse secant function is ...

$\left[0,\frac{\pi}{2}\right) \cup \left(\frac{\pi}{2} , \pi\right]
$

get an angle co-terminal with $\theta = -\frac{9\pi}{7}$ that is in the range of the inverse secant function ...

$\sec\left(-\frac{9\pi}{7}\right) = \sec\left(\frac{5\pi}{7}\right)$

$arcsec\left[\sec\left(\frac{5\pi}{7}\right)\right] = \frac{5\pi}{7}$
• Sep 24th 2009, 04:40 PM
kevintrung
Quote:

Originally Posted by skeeter
you need to know that the range of the inverse secant function is ...

$\left[0,\frac{\pi}{2}\right) \cup \left(\frac{\pi}{2} , \pi\right]
$

get an angle co-terminal with $\theta = -\frac{9\pi}{7}$ that is in the range of the inverse secant function ...

$\sec\left(-\frac{9\pi}{7}\right) = \sec\left(\frac{5\pi}{7}\right)$

$arcsec\left[\sec\left(\frac{5\pi}{7}\right)\right] = \frac{5\pi}{7}$

thanks i think i got it now, my professor is so rush in this stuff