(50+1)(50-1) = 2500 -1 = 2499
(82-81)(82+81) = 163
a) 51x49
=( 50+1) x(50-1)
=50x50 -1x1
=2500-1=2499
b) 822-812
=(82-81)x (82+81)
=1x 163
=163
Tính nhanh
51 x 49
b) 822 - 812
a) 51x49
=( 50+1) x(50-1)
=50x50 -1x1
=2500-1=2499
b) 822-812
=(82-81)x (82+81)
=1x 163
=163