A. 102 x 98
=> (6 x 17) x (2 x 49)
=> (6 x 2)(17 x 49)
=> (6 x 2)(49 x (10 + 7))
=> (6 x 2)(490 + 343)
=> (6 x 2) x 833 =  6 x 1666 = 9996
b. 1003 x 97
=> 1003 x (30 + 30 + 30 + 7)
=> 30090 + 30090 + 30090 + 7051
=> 90270 + 7051 = 97321
c. 205²
=> (5 x 41)²
=> 25 x (41)²
=> 5 x (20 + 20 + 1) x 5 x (20 + 20 + 1)
=> (100 + 100 + 5) x (100 + 100 + 5)
=> (200 + 5) x (200 + 5)
Bentuk perkalian seperti (a + b) x (a + b) = a² + ab + ab + b² = a² + 2ab + b²
=> 40000 + 2(200 x 5) + 25
=> 40000 + 2000 + 25
=> 42025
d. 398²
=> (2 x 199)²
=> 4 x (199)²
=> 2 x (100 + 80 + 19) x 2 x (100 + 80 + 19)
=> (200 + 160 + 38) x (200 + 160 + 38)
=> 40000 + 32000 + 7600 + 32000 + 25600 + 6080 + 7600 + 6080 + 1444
=> 158404