E[X] = 1*1/4 + 0*1/4 + (-1)*1/4 + 0*1/4 = 0
E[Y] = 0*1/4 + 1*1/4 + 0*1/4 + (-1)*1/4 = 0
E[(X-0)(Y-0)] = (1*0)*1/4+(0*1)*1/4+((-1)*0)*1/4 + (0*(-1))*1/4

こんくらいでいいか?