stopandthink Posted October 19, 2012 Share Posted October 19, 2012 [math] y= x^3[/math] [math] y+dy= (x+dx)^3 [/math] My question is how would i go about cubing x+dx? I can use the foil method easily with squaring, but i can't quite see how on this. Link to comment Share on other sites More sharing options...
Greg H. Posted October 19, 2012 Share Posted October 19, 2012 You have to FOIL twice, basically. So you do (x+dx) * (x+dx) then multiply the product by (x+dx) again. My question is why are you bothering to do all this work when a simple application of the product rule will get the result you need. Link to comment Share on other sites More sharing options...
stopandthink Posted October 19, 2012 Author Share Posted October 19, 2012 (edited) Like this? [math] x^2+dx(x)+dx(x)+dx^2(x+dx) [/math] ---I have absolutely no clue as to what to do next Edited October 19, 2012 by stopandthink Link to comment Share on other sites More sharing options...
Greg H. Posted October 19, 2012 Share Posted October 19, 2012 Like this? [math] x^2+dx(x)+d(x)+dx^2(x+dx) [/math] Yeah, though I would write it like this to avoid confusion [math] (x^2+2dx(x)+dx^2)\times(x+dx) [/math] Link to comment Share on other sites More sharing options...
stopandthink Posted October 19, 2012 Author Share Posted October 19, 2012 (edited) Yeah, though I would write it like this to avoid confusion [math] (x^2+2dx(x)+dx^2)\times(x+dx) [/math] Could you explain how to use the foil method on this? ------------------------------------------------------------------------- I'm just going to review the binomial theorem. Edited October 19, 2012 by stopandthink Link to comment Share on other sites More sharing options...
Greg H. Posted October 19, 2012 Share Posted October 19, 2012 Could you explain how to use the foil method on this? ------------------------------------------------------------------------- I'm just going to review the binomial theorem. It's not really FOIL at this point. It's just brute force multiplication. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now