Expansion of exponentials (very easy)

1. Apr 30, 2008

Crosshash

Sorry, i'm having a severe mental block here, sorry if this is laughable.

Question
Expand (e^x + e^-x)^2

I've got the answer but i'm just stumped at how to reach it, I dunno where the 2 comes from:

e^2x + 2 + e^-2x

Thanks (and sorry again)

2. Apr 30, 2008

eok20

Are you unsure how to even start or is there a particular term you are confused about? Which 2 are you talking about, the +2 or the 2 in e^2x?

3. Apr 30, 2008

Crosshash

Sorry, the +2. I can reach the e^2x + e^-2x but I can't reach the "+2" which means the method I'm using is incorrect.

I haven't touched this stuff in a while so I'm just trying to re-remember it.

4. Apr 30, 2008

eok20

Remember, (a+b)^2 = a^2 + 2ab + b^2 (use foil), NOT a^2 + b^2

5. Apr 30, 2008

Crosshash

Yeah, i tried using foil.

Foil if I'm not mistaken would grant me.

(e^x + e^-x) (e^x + e^-x)

(e^x * e^x) + (e^x * e^-x) + (e^-x * e^x) + (e^-x * e^-x)

(e^2x) + (1) + (1) + (e^-2x)

(e^2x) + (2) + (e^-2x)

Is that right?

6. Apr 30, 2008

eok20

Yep, looks good.

7. Apr 30, 2008

Crosshash

aha, thanks for the help. Just got a bit confused with the powers for a moment it seems.