Suppose (X,Y) follows bivariate normal distribution with means μ1,μ2, standard deviations σ1,σ2 and correlation coefficient ρ, where all the parameters are unknown. Then testing H0:σ1=σ2 is equivalent to testing the independence of
1. X and ˉY
2. X and X−Y
3. X+Y and Y_
4. X+Y and X−Y