101 * 99= (100+1) (100-1) = 100² -1² = 10000-1= 9999
51*49= (50+1) (50-1) = 50²-1²= 2500-1=2499
61*59= ( 60+1) (60-1)= 60²-1²= 3600-1= 3599
102*98= (100+2) (100-2) = 100²-2²= 10000-4= 9996
32*28= (30+2)(30-2)= 30²-2²= 900-4= 896
43*37= (40+3) (40-3) = 40²-3²= 1600-9= 1591