Solving a trigonometric equation

Printable View

April 26th 2009, 08:35 AM
blue_blue

Solving a trigonometric equation

sin a + sin 3a = cos a + cos 3a
April 27th 2009, 07:32 AM
red_dog

Use $\sin a+\sin b=2\sin\frac{a+b}{2}\cos\frac{a-b}{2}$ and $\cos a+\cos b=2\cos\frac{a+b}{2}\cos\frac{a-b}{2}$

Then,

$2\sin 2a\cos a=2\cos 2a\cos a$

$2\cos a(\sin 2a-\cos 2a)=0$

Now you have to solve the equations:

$\cos a=0$ and $\sin 2a-\cos 2a=0\Leftrightarrow \tan 2a=1$

Can you do that?

All times are GMT -8. The time now is 11:43 AM.

Copyright © 2005-2013 Math Help Forum. All rights reserved.

Copyright © 2005-2013 Math Help Forum. All rights reserved.