Question

bài 1

C=1+3+3^2+3^3+...+3^11

Answer 1

= 3(1 + 3 + 3^2 + 3^3 + .....+ 3^11)

= 3 + 3^2 + 3^3 + ...+ 3^12

=> Ta lấy 3C - C = (3 + 3^2 + 3^3 +...+ 3^12) - (1 + 3 + 3^2 +...+ 3 ^11)

= 3^12 - 1

=> C = (3^12 - 1) : 2

k mình nha bạn!

Answer 2

C = 1 + 3 + 3² + 3³ + ... + 3¹¹

3C = 3 + 3² + 3³ + 3⁴ + ... + 3¹²

3C - C = ( 3 + 3² + 3³ + 3⁴ + ... + 3¹² ) - ( 1 + 3 + 3² + 3³ + ... + 3¹¹ )

2C = 3¹² - 1

C = \(\frac{3^{12}-1}{2}\)