Câu hỏi của Do Duc Bao Lam

Question

Cứu:)))

A) S = 2 + 2² + 2³ +..... + 2²⁰

B) A= 5 + 5² + 5³ + .....+ 5⁹⁶

boi đz · Accepted Answer

$a.S=2+2^2+2^3+...+2^{20}\2S=2^2+2^3+...+2^{21}\

2S-S=\left(2^2+2^3+...+2^{21}\right)-\left(2+2^2+2^3+...+2^{20}\right)\
S=2^{21}-2\
b,A=5+5^2+5^3+...+5^{96}\
5A=5^2+5^3+5^4+.......+5^{97}\
5A-A=\left(5^2+5^3+...+5^{97}\right)-\left(5+5^2+5^3+...+5^{96}\right)\
4A=5^{97}-5\
A=\dfrac{5^{97}-5}{4}$Câu trả lời: $a.S=2+2^2+2^3+...+2^{20}\2S=2^2+2^3+...+2^{21}\

2S-S=\left(2^2+2^3+...+2^{21}\right)-\left(2+2^2+2^3+...+2^{20}\right)\
S=2^{21}-2\
b,A=5+5^2+5^3+...+5^{96}\
5A=5^2+5^3+5^4+.......+5^{97}\
5A-A=\left(5^2+5^3+...+5^{97}\right)-\left(5+5^2+5^3+...+5^{96}\right)\
4A=5^{97}-5\
A=\dfrac{5^{97}-5}{4}$

Nguyễn Đức Trí · Answer

$S=2+2^2+2^3+...+2^{20}$

$\Rightarrow S=2\left(1+2^1+2^2+...+2^{19}\right)$

$\Rightarrow S=2.\dfrac{2^{19+1}-1}{2-1}=2\left(2^{20}-1\right)$

$B=5+5^2+5^3+...+5^{96}$

$\Rightarrow B=5\left(1+5^1+5^2+...+5^{95}\right)$

$\Rightarrow B=5.\dfrac{5^{95+1}-1}{5-1}=\dfrac{5\left(5^{96}-1\right)}{4}$Câu trả lời: $S=2+2^2+2^3+...+2^{20}$

$\Rightarrow S=2\left(1+2^1+2^2+...+2^{19}\right)$

$\Rightarrow S=2.\dfrac{2^{19+1}-1}{2-1}=2\left(2^{20}-1\right)$

$B=5+5^2+5^3+...+5^{96}$

$\Rightarrow B=5\left(1+5^1+5^2+...+5^{95}\right)$

$\Rightarrow B=5.\dfrac{5^{95+1}-1}{5-1}=\dfrac{5\left(5^{96}-1\right)}{4}$

Chúng tôi đề xuất

Tài nguyên

Ứng dụng mobile

Bảng xếp hạng

Các khóa học có thể bạn quan tâm

Yêu cầu VIP