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How to use "Solve" to get only real number solutions?

• To: mathgroup at smc.vnet.net
• Subject: [mg55132] How to use "Solve" to get only real number solutions?
• From: "PengYu.UT at gmail.com" <PengYu.UT at gmail.com>
• Date: Sun, 13 Mar 2005 04:57:54 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

Hi All

For example I have the following function and I want to find the
solution of the quation shown below. But Mathematica showns not only
real number solutions. Do you know how to restrict the solutions to
only real numbers. Thanks!

Best wishes,
Peng

intensity[x_, δ_, p_, λ_] := 1/4 + (2*Cos[(Pi*x)/100])/Pi +
(4*Cos[(Pi*x)/100]^2)/Pi^2 - (2*Cos[(3*Pi*x)/100])/(3*Pi) -
 (8*Cos[(Pi*x)/100]*Cos[(3*Pi*x)/100])/(3*Pi^2) +
(4*Cos[(3*Pi*x)/100]^2)/(9*Pi^2)

Solve[intensity[x, 0, 200, 50] == 0.3*(1/4 + 32/(9*Pi^2) +
(4*Sqrt[2])/(3*Pi)), x]