Tính cách hợp lý: A = (1 × 2 + 2 × 3 + 3 × 4 +.....+ 9 × 10) × (2⁵ - 2⁴ - 2³ - 2² - 2 - 2)

B = 1 x 2 + 2 x 3 + 3 x 4 +...+ 9 x 10

3B= 1 x 2 x 3 + 2 x 3 x 3 + 3 x 4 x 3 +...+ 9 x 10 x 3

3B = 1 x 2 x 3 + 2 x 3 x (4 - 1) + 3 x 4 x (5 - 2) +...+ 9 x 10 x (11 - 8)

3B = 1 x 2 x 3 + 2 x 3 x 4 - 1 x 2 x 3 + 3 x 4 x 5 - 2 x 3 x 4 +...+ 9 x 10 x 11 - 8 x 9 x 10

3B = 9 x 10 x 11

=> B = (9 x 10 x 11) : 3 = 330

C = 2⁵ - 2⁴ - 2³ - 2² - 2 - 2

= 2⁵ - 2⁴ - 2³ - 2² - 4

= 2⁵ - 2⁴ - 2³ - 2² - 2²

= 2⁵ - 2⁴ - 2³ - 2³

= 2⁵ - 2⁴ - 2⁴

= 2⁵ - 2⁵

= 0

=> A = B x C

= 330 x 0

= 0

B = 1 x 2 + 2 x 3 + 3 x 4 +...+ 9 x 10

3B= (1 x 2 x 3) + (2 x 3 x 3) + (3 x 4 x 3) +...+ (9 x 10 x 3)

3B = (1 x 2 x 3) + 2 x 3 x (4 - 1) + 3 x 4 x (5 - 2) +...+ 9 x 10 x (11 - 8)

3B = (1 x 2 x 3) + (2 x 3 x 4) - (1 x 2 x 3) + (3 x 4 x 5) - (2 x 3 x 4) +...+ (9 x 10 x 11) - (8 x 9 x 10)

3B = 9 x 10 x 11

=> B = 330

C = 2⁵ - 2⁴ - 2³ - 2² - 2 - 2

= 2⁵ - 2⁴ - 2³ - 2² - 2²

= 2⁵ - 2⁴ - 2³ - 2³

= 2⁵ - 2⁴ - 2⁴

= 2⁵ - 2⁵

= 0

=> A = B x C = 0