The Purplemath Forums

Hi this is my first post here. First off I want to express my immeasurable gratitude to this site as it has helped me a lot. I have a question about as my thread title states, the sum and difference of cubes. The sample question to factor x 3 y 6 – 64 confuses me. I tend to over think things in math...

I think I figured it out on my own. x³y⁶ becomes (xy²)³ because the three is getting factored out right? I hope that's right :l.

From what I understand there's a difference of opinions when it comes to this. Some people look at it as -(x^2) and others -x^2. Both give different answers which is why I'm asking what should I do when I have something like in front of me?

Wouldn't -x² mean -x * -x which would result in a positive? Compared to -(x²), for the sake of this lets say x is 2. So -(2²) = -(4) = -4.

Ah ok. Thanks .

Something about the lesson given here confuses me. I understand how to complete the square, but this is bothering me and I need to know why this happens. So we have sample question 4x 2 - 2x - 5 = 0 I understand everything up until I have to convert the left side to squared form, let me show you why...

stapel_eliz wrote:

geramul wrote:x² - 1/2x + 1/16 = 5/4 + 1/16.

Now we have (x - 1/4)² = 21/16

My question is, what happened to the 1/16 on the left side?

What is (x - 1/4)² equal to, after expansion?

Ahhhhhh I see. I hate and love math because of tricky dicky shit like this lol. Thanks.

Ugh. This is a stupid question, but unfortunately it's impossible for me to let this go until I know the answer. Alright, i goes in a pattern yes? i 0 = 1 i 1 = i i 2 = -1 i 3 = -i i 4 = 1 And so on. Now for the question :roll: I see a lot that the reason i 4 = 1 is as follows. (i 3 )(i 1 ) = i 4 Si...

I think I get it now, thanks. I get stuck on the stupidest stuff sometimes :P.

I have only one question for this. Let me write out where I got stuck. (x + b/2a) 2 = -c/a + b 2 /4a 2 What I can't figure out is how the common denominator of 4a is gotten. Let me give an example. Lets say we want to add together 1/4 and 5/8. We would look of course at the multiples of 4 and find o...