hello to all. this is my first time here. I hope you can help me on this:

1) Find th measure of the group
{x belongs to R: f(x)=1/(1+x^2)<a}, a>0

2) prove that the function is measurable:

f(x)= if x=p/q rational number then f(x)=1/q
= if x is irrational number then f(x)=0

I know it's a little hard, but I am having hard time with it.
thanks to all !!!

my email is: te100@walla.co.il