Question

A =2+2^2+2^3+...+2^20

B=1+5+5^2+5^3+...+5^30

Nhanh lên nha mn

Answer 1

Ta có:A=2+2²+2³+...+2²⁰

=>2A=2(2+2²+2³+...+2²⁰)

2A=4+2³+2⁴+...+2²¹

=>2A-A=(4+2³+2⁴+...+2²¹)-(2+2²+2³+...+2²⁰)

A=2²¹-2

Answer 2

A= 2.( 2+ 2+ 3+ 4+ 5+ 6+ 7+8 +9 + 10= 11+ 12+ 13+ 14+15+ 16+ 17+ 18+ 19+ 20)

A=2.211

A= 422

B= 5.(1+ 5+ 2+ 3+ 4+ 5+ 6+ 7+ 8+ 9+..........+30)

B= 5. 470

B= 2350 

Answer 3

Ta có:B=1+5+5²+5³+...+5³⁰

=>5B=5(1+5+5²+...+5³⁰)

5B=5+5²+5³+...+5³¹

=>5B-B=(5+5²+5³+...+5³¹)-(1+5+5²+...+5³⁰)

4B=5³¹-1

=>B=5³¹-1/4

Answer 4

Bài 1:

A=2+2²+2³+...+2²⁰

2A=2²+2³+...+2²⁰+2²¹

A=\(2^{21}-2\)

Vậy ....

Bài 2:

B=1+5+5²+...+5³⁰

5B=5+5²+...+5³⁰+5³¹

4B=5³¹-1

B=\(\frac{5^{31}-1}{4}\)

Vậy .....