Re: new user help

*To*: mathgroup at smc.vnet.net*Subject*: [mg13328] Re: new user help*From*: Arnoud Buzing <arnoudb>*Date*: Mon, 20 Jul 1998 02:49:50 -0400*Organization*: Wolfram Research, Inc.*References*: <6okkvj$1md@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

John M. Dlugosz wrote: > > I'm lost. I just don't know how to get started... > > The excersize I've chosen for myself is to start with > > x^2+y^2+4x-6y+4==0 > > and manipulate it into the form (x-h)^2+(y-k)^2==r^2 > > So... how do I "manipulate" the equasion? The functions like Expand, > Factor, etc. don't help much. I my calculator (an HP48) I can point to > specific subexpressions and apply operations to them, like factor, > distribute, changing forms, etc. > > How do I collect the x's together in parens, the y's in parens, and > complete the squares? Doing it on paper defeats the point! I want to > learn how to "do math" using this tool. That's more than just asking > "OK, what's X?". It means manipulating things and arranging them, > getting to know how the symbols all fit together. > > --John This may help: x^2 + y^2 + 4x - 6y + 4 == 0 //. {t_^2 + b_ t_ -> (t + b/2)^2 - b^2/4} The //. is short for ReplaceRepeated, which means it will apply the rule on the right until there is nothing left to replace. The { ... -> ... } is a replacement rule. In this case it will look for things that look like t^2+bt and replace it by what you suggested. (See also section 2.4 in the Mathematica book). --- Arnoud