a² - b²=(a-b)(a+b)
.
55²- 45²=(55-45)(55+45)=10*100=1000
64²- 36²=(64-36)(64+36)=28*100=2800
86²- 14²=(86-14)(86+14)=72*100=7200
328²- 172²=(328-172)(328+172)=156*500=78000
(3 2/3)²- (2 1/3)²=(3 2/3 - 2 1/3)(3 2/3+2 1/3)=1 1/3 * 6=4/3 * 6=8
(7 5/9)²- (4 4/9)²=(7 5/9 - 4 4/9)(7 5/9+4 4/9)=3 1/9 * 12=28/9 * 12=112/3=37 1/3