       Integrate problem

• To: mathgroup at smc.vnet.net
• Subject: [mg65493] Integrate problem
• From: "axman" <yuerlong at gmail.com>
• Date: Wed, 5 Apr 2006 06:55:37 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```Hi, Group
I am new to Mathematica and now meet one problem I can't solve by
self.  First I defined 3 functions: h, f and g

\!\(\(h[t_] := \(-20\)*Cos[t] Exp[\(-t\)\/20];\)\[IndentingNewLine]
\(f[x_, y_] := Cos[x] Sin[y];\)\[IndentingNewLine]
\(g[Î±_, Î²_, t_] :=
If[t == 0, \(-1\), If[h[t] <
Î², \(-1\), If[h[t] > Î±, \(+1\), g[Î±, Î², t - 0.1]]]];\)\)

Now I try to integrate the function f[x,y]*g[x,y,10] on a triangle
region:

\!\(â?«\_\(-20\)\%20\(â?«\_\(-20\)\%x\((N[f[
x, y]\ g[x, y, 10]])\) \[DifferentialD]y \[DifferentialD]x\)\)

The output result is strange. How to get correct answer for this
integration?

Thank you for help.

```

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