Re: Factor and/or Rules replacements
- To: mathgroup at smc.vnet.net
- Subject: [mg104500] Re: [mg104443] Factor and/or Rules replacements
- From: "David Park" <djmpark at comcast.net>
- Date: Sun, 1 Nov 2009 17:57:34 -0500 (EST)
- References: <24397765.1257066820598.JavaMail.root@n11>
f[b_, c_] = Function[x, x^2 + b x + c] (x - Root[f[b, c], 1]) (x - Root[f[b, c], 2]) David Park djmpark at comcast.net http://home.comcast.net/~djmpark/ From: yves [mailto:yves.dauphin at solvay.com] Hello everybody, Here is the model problem: I tried to obtain the factorisation of x^2+b x +c and expected to get something like (x-1/2(-b+Sqrt[b^2-4 c))((x-1/2(-b-Sqrt[b^2-4 c)). So I tried in:Factor[x^2+b x + c] and get out: c + b x + x^2 So my first question what should I have done? I tried another way in:sol=Solve[x^2+b x + c == 0,{x}]; and get the couple of replacement rules. Next I defined in: f=(x-x1)(x-x2) and finally I replaced x1 and x2 in succession by in:f /. {(sol[[1]] /. x -> x1), (sol[[2]] /. x -> x2)} which gave the expected factorisation but enclosed in {}. My second question is : Is there a simpler way or more compact to replace x1 and x2? With anticipated thanks. Yves