... 47)(53 – 47) = 100 . 6 = 600 c. 31, 8 2 – 2 . 31, 8 . 21, 8 + 21, 8 2 = (31, 8 – 21, 8) 2 = 10 2 = 100 d, 58, 2 2 + 2 . 58, 2 . 41, 8 + 41, 8 2 = ( 58, 2 + 41, 8) 2 = 100 2 = 10000 NhËn d¹ng c¸c ... -25x 6 – y 8 + 10x 3 y 4 d, 1/ 4x 2 – 5xy + 25y 2 Bµi tËp 3: TÝnh nhanh a. 75 2 – 25 2 c, 31, 8 2 – 2 . 31, 8 . 21, 8 + 21, 8 2 b. 53 2 – 47 2 d, 58, 2 2 + 2 . 58, 2 . 41, 8 + 41, 8 2 Bµi tËp ... Híng dÉn: Bµi tËp 3: TÝnh nhanh a. 75 2 – 25 2 c, 31, 8 2 – 2 . 31, 8 . 21, 8 + 21, 8 2 b. 53 2 – 47 2 d, 58, 2 2 + 2 . 58, 2 . 41, 8 + 41, 8 2 a. 75 2 – 25 2 = (75 + 25)(75 – 25) = 100 . 50 =...