21111102

= 111111102

111111102

9 . 1 + 9. 11 + 9.111 + 9.1111 + 9.11111 + 9.111111 + 9.1111111 + 9.11111111 + 9.111111111 + 9.1111111111

= (10-1) + (100 -1) + (1000-1) + (10000-1) + ............+ (10000000000-1)

= ( 10+100+1000+10000+..........+10000000000) - (1+1+1+1+..........+1+1)

=11111111110 - 1.10

=1111111100

= (10-1) + (100 -1) + (1000-1) + (10000-1) + ............+ (10000000000-1)

= ( 10+100+1000+10000+..........+10000000000) - (1+1+1+1+..........+1+1)

=11111111110 - 1.10

=1111111100

11111111110-1.10

= 1111111100

9 + 99 + 999 + .....+ 9999999999.......9999999(có 100 c/s 9)

=10-1+10²-1+10³-1+...+10¹⁰⁰-1

=10+10²+10³+..+10¹⁰⁰+(-1-1-1-...-1(100 chữ số 1))

=10+10²+10³+...+10¹⁰⁰-100

Đặt : A=10+10²+10³+...+10¹⁰⁰

=>10A=10²+10³+...+10¹⁰¹

=>10A-A=10²+10³+...+10¹⁰¹-10-10²-10³-...-10¹⁰⁰

=>9A=10¹⁰¹-10

=>A=\(\frac{10^{101}-10}{9}\)

suy ra: 9 + 99 + 999 + .....+ 9999999999.......9999999(có 100 c/s 9)

=\(\frac{10^{101}-10}{9}-10^2-\frac{10^{101}-10}{9}-100\)

bài này vẫn có cách tính

Bạn tính đi.

=-4444444

-4444444

-4444444

Ta có

kết quả là: 

9999999 - 9999999

= 0

nha bn

9999999 - 9999999 =0

nha bn k mk nha bn

thanks nhju

9999999 - 9999999 = 0

quy dồng mẫu lên 6 rồi bấm máy mà trừ

\(H=\frac{9999999}{2}-\frac{9999999}{3}-\frac{9999999}{6}\)

\(\Rightarrow H=9999999.\left(\frac{1}{2}-\frac{1}{3}-\frac{1}{6}\right)\)

\(\Rightarrow H=9999999.0\)

\(\Rightarrow H=0\)