Re: How to evaluate a NIntegrate expression properly

*To*: mathgroup at smc.vnet.net*Subject*: [mg39739] Re: How to evaluate a NIntegrate expression properly*From*: Bill Rowe <listuser at earthlink.net>*Date*: Mon, 3 Mar 2003 23:52:04 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

On 3/3/03 at 4:24 AM, hardes at MIT.EDU (Yong Xiao) wrote: >Hi, I have a problem regarding to how to use NIntegrate and NSolve >together. A sampe is as follwing: >f[y_] := NIntegrate[y^2*x^2, {x, 0, 3}] >NSolve[f[y] == 20, y] NIntegrate is designed to return a numerical answer. It cannot do this unless all variables are assinged numerical values. f[y] fails since y is not assigned a numerical value. If f[y] did not fail, that is it returned a numerical value, NSolve would fail since there would be no variable y in the equation. Try NSolve[Integrate[y^2 x^2, {x, 0, 3}] == 20, y]