12+12+12+13+13+13+2222+2222+3^4=4600

4600 nha chị/anh

9/13 x 7/12 + 9/13 x 5/12 - 9/13

= 9/13 x (7/12 + 5/12 - 1)

= 9/13 x 0

= 0

4/13 x 5/12 + 4/13 x 7/12 - 4/3

= 4/13 x (5/12 + 7/12) - 4/3

= 4/13 x 1 - 4/3

= 4/13 - 4/3

= -40/39

a) 9/13 x 7/12 + 9/13 x 5/12 - 9/13

= 9/13 x ( 5/12 + 7/12 - 1 )

= 9/13 x 0

= 0

b) 4/13 x 5/12 + 4/13 x 7/ 12 - 4/3

= 4/13 x ( 5/12 + 7/12 - 13/3 )

= 4/13 x ( - 10/3 )

= -40/39 

a) \(\frac{9}{13}\cdot\frac{7}{12}+\frac{9}{13}\cdot\frac{5}{12}-\frac{9}{13}\)

\(=\frac{9}{13}.\left(\frac{7}{12}+\frac{5}{12}-1\right)=\frac{9}{13}.\left(1-1\right)=\frac{9}{13}.0=0\)

b) \(\frac{4}{13}\cdot\frac{5}{12}+\frac{4}{13}\cdot\frac{7}{12}-\frac{4}{3}\)

\(=\frac{4}{13}.\left(\frac{5}{12}+\frac{7}{12}\right)-\frac{4}{3}=\frac{4}{13}.1-\frac{4}{3}=\frac{4}{13}-\frac{4}{3}\)

1) = \(\frac{3}{5}\)

2) =\(\frac{6}{7}\)

3)\(\frac{9}{13}\)

4)\(\frac{4}{13}\)

1/13+2/13+....+12/13

=1+2+3+..+12/13

=(12+1)x12:2/13

=13x12:2/13

=156:2/13

=78/13=6

ồ cuk dễ nhỉ

Nếu các bn thích thì ...........

cứ cho NTN này nhé !

\(\frac{1}{13}+\frac{2}{13}+\frac{3}{13}+...+\frac{10}{13}+\frac{11}{13}+\frac{12}{13}\) 

\(\frac{1+2+3+...+10+11+12}{13}\)

\(\)khoảng cách 2-1=1

số số hạng :(12-1)/1+1=12(số)

tổng dãy số :\(\frac{\left(12+1\right)\cdot12}{2}=78\)

vậy 1/13+2/13+3/13+..10/13+11+13+12/13=78/13

Câu a đề sai rồi bạn

b: \(3+3^2+3^3+...+3^{16}\)

\(=3\left(1+3\right)+3^3\left(1+3\right)+...+3^{15}\left(1+3\right)\)

\(=4\left(3+3^3+...+3^{15}\right)\)

\(=12\left(1+3^2+...+3^{14}\right)⋮12\)

=(1/13+12/13)+(2/13+11/13)+(3/13+10/13)+......(6/13+7/13)

=1+1+1+1+1+1

=6

\(=\frac{1+2+3+...+12}{13}\)

\(=\frac{\left(12+1\right)+\left(11+2\right)+..+\left(5+7\right)+6}{13}\)

\(=\frac{12+12+12+12+12+6}{13}\)

\(=\frac{12.5+6}{13}\)

\(=\frac{66}{13}\)

Cảm ơn bạn nhiều nhé!!!