toán lớp 2

bt ko mà nói ^^

tui ghét lũy thừa nên lười

mik cx ko bt câu này

mik cx dg định đăng câu này

hok tốt

cs chép sai đè ko vậy

không

tự giải đi

tự làm đi cho biết hỏi làm gì

\(S=1+2+2^2+2^3+2^4+2^5+2^6+2^7\)

\(\Rightarrow S=\left(1+2\right)+\left(2^2+2^3\right)+\left(2^4+2^5\right)+\left(2^6+2^7\right)\)

\(\Rightarrow S=\left(1+2\right)+2^2\left(1+2\right)+2^4\left(1+2\right)+2^6\left(1+2\right)\)

\(\Rightarrow S=\left(1+2\right)\left(1+2^2+2^4+2^6\right)\)

\(\Rightarrow S=3\left(1+2^2+2^4+2^6\right)⋮3\)

S=(1+2)+...+2^6(1+2)=3(1+...+2^6)⋮3

\(S = 1 + 2 + 2^{2} + 2^{3} + 2^{4} + 2^{5} + 2^{6} + 2^{7}\)

\(\Rightarrow S = \left(\right. 1 + 2 \left.\right) + \left(\right. 2^{2} + 2^{3} \left.\right) + \left(\right. 2^{4} + 2^{5} \left.\right) + \left(\right. 2^{6} + 2^{7} \left.\right)\)

\(\Rightarrow S = \left(\right. 1 + 2 \left.\right) + 2^{2} \left(\right. 1 + 2 \left.\right) + 2^{4} \left(\right. 1 + 2 \left.\right) + 2^{6} \left(\right. 1 + 2 \left.\right)\)

\(\Rightarrow S = \left(\right. 1 + 2 \left.\right) \left(\right. 1 + 2^{2} + 2^{4} + 2^{6} \left.\right)\)

\(\Rightarrow S = 3 \left(\right. 1 + 2^{2} + 2^{4} + 2^{6} \left.\right) 3\)

a: \(A=2\left(1+2+2^2\right)+...+2^{19}\left(1+2+2^2\right)\)

\(=7\left(2+...+2^{19}\right)⋮7\)

tự làm nha

1. Chứng minh rằng: 3^2+3^3+3^4+...+3^101 chia hết cho 120.

Ta có:

A=3^2+3^3+3^4+...+3^101 

= (3^2+3^3+3^4+3^5) + ( 3^6+3^7+3^8+3^9) +.... + ( 3^98 + 3^99 + 3^100 + 3^101)

= 3.(3+3^2+3^3+3^4) + 3^5.(3+3^2+3^3+3^4) +....+ 3^97.(3+3^2+3^3+3^4)

= 120.(3+3^5+...+3^97) chia hết cho 120

a: \(A=2\left(1+2+2^2\right)+...+2^{19}\left(1+2+2^2\right)\)

\(=7\left(2+...+2^{19}\right)⋮7\)

a: \(A=2\left(1+2+2^2\right)+...+2^{19}\left(1+2+2^2\right)\)

\(=7\cdot\left(2+...+2^{19}\right)⋮7\)