# Last Class Help!!

• Jun 2nd 2008, 09:09 AM
Dave53
Last Class Help!!
I'm taking my last class for my bachelors and of'course it's my worst class, trigonometry.

Can anybody help me with this problem?

"Show the counter example that the following equation is not an identity?"

(sin x+ cos x)2=sin2x+cos2x (The "2"s are squares)

Thanks for the help!
Dave
• Jun 2nd 2008, 09:23 AM
o_O
You just need a counter-example? Many examples work really. Chances are if you pick a random value for x off the top of the head, you would have a counter example. For example, $\displaystyle x = \frac{\pi}{3}$:

$\displaystyle \left[ \sin \left(\frac{\pi}{3}\right) + \cos \left(\frac{\pi}{3}\right) \right]^{2} = \left(\frac{\sqrt{3}}{2} + \frac{1}{2}\right)^{2} = ... \neq 1$ (since $\displaystyle \sin^{2} x + \cos^{2} x = 1$)
• Jun 2nd 2008, 11:28 AM
Dave53
Thanks.

As you may have figured out; math is not my favorite or best subject. Being out of school for 30+ years doesn't help either.

I think I'll be back several more times for help.