Differential function to plot

The problem :

consider u"(x) + 9u = f(x) ;

u(0) = u'(1) = 0 , where f is a Differential function on [0,1] .

so how can i plot this function ?

[Diaa]

I couldn't find this form you share. Do you mean you have something like

d2y/dx2 = 9*x

?

[fatima azway]

[fatima azway]

look at example 2.2

this one what i want to plot