Plot PDF's for N samples.

Hi I have a binary hypothesis test where I observe 20 samples which are iid ( independent and identically distributed). Under the null hypothesis I am assuming that the 20 samples each follow a normal distribution with mean 0 and variance of 1. Also for the alternate hypothesis, I am assuming that the 20 samples each follow a normal distribution with mean 0 and variance of 2. This is the result, representing the sample by x[n]:

and

Above gives the PDF for each sample, and since they are iid the joint density function for each hypothesis becomes:

and

Where Π represents the products of the individual PDFs. How can I plot the joint density functions, and in MATLAB.