Problem with Statistics/probability/calculus?

[roadrunner]

Homework Statement

let X denote the vibratory stress (psi) on a wind turbine at a certain wind speed. the pdf is

f(x;y) = (x/y^2)*(e^((-x^2)/(2y^2))

a) i need to prove that it is a pdf.
b)assume y=100, what is the probabilty X is at most/least 200? what's prob X les than 200

Homework Equations

The Attempt at a Solution

so i did part a part 1...f(x;y) is greter than 0 for all values...
but for the integral of f(x)=1, i think i need to know how to integrate that, and i have no idea how!

 

[Dick]

Try the substitution u=x^2/(2*y^2).

 

[roadrunner]

y is a constant tho?

 

[EnumaElish]

I think y is constant.

 

[Dick]

y is a constant tho?

Sure. You said you were integrating dx, right? y is just a parameter.