Question

[Lê Trọng Chương]

1. Tính            A = 1.99+2.98+3.97+...+49.51+50.50

   2. Tính            B = 1.3+5.7+9.11+...+97.101

   3. Tính             C = 1.3.5-3.5.7+5.7.9-7.9.11+...-97.99.101

   4. Tính             D = 1.99+3.97+5.95+...+49.51

   5. Tính              E = 1.3³+3.5³+5.7³+...+49.51³

   6. Tính             F = 1.99²+2.98²+3.97²+...+49.51²

​ai đúng mình ủng hộ

Answer 1

[Le_Bich_Dao]

1/ A= 1.(100-1)+2(100-2)+3.(100-3)+...+49.(100-51)+50.(100-50)

      = 1.100-1+2.100 - 2.2 + 3.100 -3.3 + ...+49.100 - 49.51 + 50.100 - 50.50

      = 100( 1 + 2 + 3 + ...+ 50) - ( 1 + 2² + 3² + ... + 50² )

      = 127500- 42925

      = 84575

Answer 2

[Le_Bich_Dao]

2/ A= 1.3 + 5.7 + 9.11+ 13.15 + 17.19 + ... + 97. 101

= 1.3 + 5(6 + 1) +9( 6+ 5) + 13(6+9) + 17(6+13) + ... + 97(95+6)

= 3 + 5.6 + 1.5 + 9.6 + 5.9 + 13.6 + 9.13 + 17.6 + 13.17 + ... + 95.97 + 97.6

= 3 + ( 1.5 + 5.9 + 9.13 + 13.17 + ...+ 95.97) + 6( 5 + 9 + 13 + 17 + ... + 97)

= ...

=\(\frac{509447}{6}\)