Tentukan dua bentuk aljabar yang bila dikalikan hasilnya adalah a) 102 × 98 b) 1.003 × 97 c) 205² d) 389²

a) 102 × 98
= (100+2)(100-2)
= (100)^2 -(2)^2
= 10.000 - 4
= 9.996
b) 103 × 97
= (100+3)(100-3)
= (100)^2 -(3)^2
= 10.000 - 9
= 9.991
c) 205^2
= (200+5)^2
= (200)^2 + 2.100.5 + (5)^2
= 40.000 + 1.000 + 25
= 41.025
d) 389^2
= (400 -11)^2
= (400)^2 -2.400.11 + (11)^2
= 160.000 - 8.800 + 121
= 151.321