Show that S^2subp is an unbiased estimator of (sigma)^2 and find its variance under the condition of following theorem. If xbar1,xbar2, s1, and s2 are the values of the means and the standard deviations of independent random samples of sizes n1 and n2 from normal population with equal variances , then (xbar1-xbar2)-talpha/2,n1+n2-2*ssubp sqrt(1/n1+1/n2)