How do i find the x value for a GIVEN x

I made a secant script for the function f = @(x) exp(1)/3*x*exp(-x/3) aslo read as (e/3)*x*e^(-x/3). How do i find the x value corisponding to y= .25. I must make a second script. I graphed the fuction on my computer and it is not a root so how do i go about this issue? I know its 11.08 but how do i write it in code?

Answer 1

[madhan ravi]

fsolve(@(x)f(x)-.25,[0,10]) % two solutions but look into you're area of interest
fplot(@(x)f(x)-.25,[0,11])

[madhan ravi]

If you have optimisation toolbox use fsolve() else use fzero()

[Nora Ahmed]

In my code I used the funtion [p,conv]=secant(f,p0,p1,TOL,max_iter) with sucessful convergence =1 and no convergence =0 i know this method is used to find roots using two points. however rather than finding f(x)=0 i need f(x)=.25 using this menthod and not the > fzero(@(x)f(x)-.25,[-1,1]) if we plotted a f(x)=.25 then we would get two points where it would intersect. I am just lost on how to go about this issue.