Let (X,Y)(X, Y)(X,Y) be uniformly distributed on the disk x2+y2≤1x^2 + y^2 \le 1x2+y2≤1. What is the marginal PDF of R=X2+Y2R = \sqrt{X^2 + Y^2}R=X2+Y2?
fR(r)=2rf_R(r) = 2rfR(r)=2r for 0≤r≤10 \le r \le 10≤r≤1
fR(r)=πrf_R(r) = \pi rfR(r)=πr for 0≤r≤10 \le r \le 10≤r≤1
fR(r)=rf_R(r) = rfR(r)=r for 0≤r≤10 \le r \le 10≤r≤1
fR(r)=1f_R(r) = 1fR(r)=1 for 0≤r≤10 \le r \le 10≤r≤1