Please help with solving trig equations!

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December 15th 2008, 12:30 PM
gobbajeezalus

Please help with solving trig equations!

http://img.skitch.com/20081215-8c2mt...2j5gm9en37.jpg

THANKS!
December 15th 2008, 01:11 PM
masters

Quote:

Originally Posted by gobbajeezalus

http://img.skitch.com/20081215-8c2mt...2j5gm9en37.jpg

THANKS!

(1) $\sin x \tan x - \sin x=0$

$\sin x(\tan x-1)=0$

$\sin x = 0 \ \ or \ \ \tan x-1=0$

$\tan x=1$

$\sin x=0 \ \ at \ \ \left\{0, \pi \right\}$

$\tan x=1 \ \ at \ \ \left\{\frac{\pi}{4}, \frac{5\pi}{4}\right\}$

Solution set= $\left\{0, \frac{\pi}{4}, \pi, \frac{5\pi}{4}\right\}$
December 15th 2008, 01:21 PM
masters

Quote:

Originally Posted by gobbajeezalus

http://img.skitch.com/20081215-8c2mt...2j5gm9en37.jpg

THANKS!

(2) $\sin 2x=-\sin x$

$\sin 2x+\sin x$

Double angle identity: $\sin 2x = 2\sin x \cos x$

$2\sin x \cos x + \sin x=0$

$\sin x(2\cos x+1)=0$

$\boxed{\sin x = 0} \ \ or \ \ 2\cos x+1=0$

$2\cos x=-1$

$\boxed{\cos x = -\frac{1}{2}}$

$\sin x=0 \ \ at \ \ \left\{0, \pi\right\}$

$\cos x = -\frac{1}{2} \ \ at \ \ \left\{\frac{2\pi}{3}, \frac{4\pi}{3}\right\}$

Solution set= $\left\{0, \pi, \frac{2\pi}{3}, \frac{4\pi}{3}\right\}$
December 15th 2008, 01:36 PM
masters

Quote:

Originally Posted by gobbajeezalus

http://img.skitch.com/20081215-8c2mt...2j5gm9en37.jpg

THANKS!

(3) $2\sin \theta \cos \theta + \sqrt{3} \sin \theta = 0$

$\sin \theta(2 \cos \theta + \sqrt{3})=0$

$\boxed{\sin \theta=0} \ \ or \ \ 2 \cos \theta = -\sqrt{3}$

$\boxed{\cos \theta = -\frac{\sqrt{3}}{2}}$

$\sin \theta = 0 \ \ at \ \ \left\{0, \pi\right\}$

$\cos \theta = -\frac{\sqrt{3}}{2} \ \ at \ \ \left\{\frac{5\pi}{6}, \frac{7\pi}{6}\right\}$

Solution set= $\left\{0, \frac{5\pi}{6}, \pi, \frac{7\pi}{6}\right\}$