Re: Assigning (really dumb question)
- To: mathgroup at smc.vnet.net
- Subject: [mg60995] Re: [mg60988] Assigning (really dumb question)
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Fri, 7 Oct 2005 03:37:40 -0400 (EDT)
- Reply-to: hanlonr at cox.net
- Sender: owner-wri-mathgroup at wolfram.com
r[q_]:=1800 q-.006 q^2; c[q_]:=12100000+800 q+.004 q^2; qa=Solve[D[r[q]-c[q],q]==0,q][[1]] r[q]/.qa c[q]/.qa r[q]-c[q]/.qa D[r[q],q]/.qa D[c[q],q]/.qa {q -> 50000.} 7.5*^7 6.21*^7 1.29*^7 1200. 1200. qm=Solve[c[q]/q-D[c[q],q]==0,q][[2]] r[q]/.qm c[q]/.qm r[q]-c[q]/.qm D[r[q],q]/.qm D[c[q],q]/.qm {q -> 55000.} 8.085*^7 6.82*^7 1.265*^7 1140. 1240. Bob Hanlon > > From: vjp2.at at at.BioStrategist.dot.dot.com To: mathgroup at smc.vnet.net > Date: 2005/10/06 Thu AM 04:08:30 EDT > Subject: [mg60995] [mg60988] Assigning (really dumb question) > > What the heck am I doing wrong? I've been away from Mathematica for a while. > > I can't get it to evaluate the expressions at the solved values. > > I feel so stupid. > > r[q_] := 1800 q - .006 q^2 > c[q_] := 12100000 + 800 q + .004 q ^2 > > qa = Solve[ D[ r[q]-c[q] , q] == 0, q] > r[q] /. q -> qa > c[q] /. q -> qa > r[q]-c[q] /. q -> qa > D[r[q],q] /. q -> qa > D[c[q],q] /. q -> qa > > qm = Solve[ c[q]/q - D[c[q] , q] == 0, q] [[2]] > r[qm] /. q -> qm > c[qm] /. q -> qm > r[qm]-c[qm] /. q -> qm > D[r[q],q] /. q -> qm > D[c[q],q] /. q -> qm > > > (PS, a while back I was asking how to fix DOS 2.2.2 when it wasn't > doing graphics and I was told it was no longer supported. Well, 2yrs > later, dumbo me, realised I just had to cd into the math directory and > all was fine.) > Bob Hanlon Chantilly, VA