# Numerical integration not working — getting error NIntegrate::inumr

For example, I want to plot a $f(y, c)=f(2, c)$ against $c$ where the function $f$ is the integral of $y \cos(c x)\,dx$ from 0 to π,

When I try to do it, I get the message:

NIntegrate::inumr: The integrand Cos[c x] has evaluated to non-numerical values for all sampling points in the region with boundaries {{0,6}}. >>

How cab I make the plot I want? I'm so lost.

Actually my function is

and this is what i want to plot

Plot[EV[4, ξ_, 2, 5, 1], {ξ, 1, 3}]

• For reference, can you show us how you tried to define f[y, c] in Mathematica? – J. M. will be back soon Mar 7 '18 at 1:24
• Plot[EV[4, ξ_, 2, 5, 1], {ξ, 1, 3}] should be Plot[EV[4, ξ, 2, 5, 1], {ξ, 1, 3}] If this change doesn't fix your problem, then you need to post your full code in markdown format (not as an image). – m_goldberg Apr 29 '18 at 4:27