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MathGroup Archive 2005

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Assigning (really dumb question)

  • To: mathgroup at
  • Subject: [mg60988] Assigning (really dumb question)
  • From: at
  • Date: Thu, 6 Oct 2005 04:08:30 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

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.)

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