\(\dfrac{-13}{4}.\dfrac{3}{7}-\dfrac{13}{4}.\dfrac{10}{7}-\dfrac{13}{7}\)

\(=\dfrac{13}{4}.\dfrac{-3}{7}-\dfrac{13}{4}.\dfrac{10}{7}-\dfrac{13}{7}\)

\(=\dfrac{13}{4}.\left(\dfrac{-3}{7}-\dfrac{10}{7}\right)-\dfrac{13}{7}\)

\(=\dfrac{13}{4}.\dfrac{-13}{7}-\dfrac{13}{7}\)

\(=\dfrac{-13}{4}.\dfrac{13}{7}-\dfrac{13}{7}\)

\(=\dfrac{13}{7}.\left(\dfrac{-13}{4}-1\right)\)

\(=\dfrac{13}{7}.-\dfrac{17}{4}\)

\(=-\dfrac{221}{28}\)

* Cách làm nhanh: Với biểu thức như trên, hai phân số nhân với nhau có thể đổi dấu cho nhau.*

-13/4 . 3/7 - 13/4 . 10/7 - 13/7

= -13/4 . (3/7 + 10/7) - 13/7

= -13/4 . 13/7 - 13/7

= 13/7 . (-13/4 - 1)

= 13/7 . (-17/4)

= -221/28

1: =-2/9(15/17+2/17)=-2/9

2: \(=\dfrac{-6}{3}+\dfrac{-21}{90}\)

=-2-7/30=-67/30

3: \(=\dfrac{3}{4}\cdot\dfrac{7}{5}+\dfrac{9}{7}\cdot\dfrac{3}{2}\)

=21/20+27/14=417/140

4: =-25/13(5/19+14/19)=-25/13

5: =-7/5-45/21=-7/5-15/7=-124/35

1: =-2/9(15/17+2/17)=-2/9

2: =34⋅75+97⋅32=34⋅75+97⋅32

=21/20+27/14=417/140

4: =-25/13(5/19+14/19)=-25/13

5: =-7/5-45/21=-7/5-15/7=-124/35

\(\frac{x}{1\cdot4}+\frac{x}{4\cdot7}+\frac{x}{7\cdot10}+\frac{x}{10\cdot13}+\frac{x}{13\cdot16}=\frac{5}{2}\)

\(\Rightarrow\frac{x}{3}\left[\frac{3}{1\cdot4}+\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+\frac{3}{10\cdot13}+\frac{3}{13\cdot16}\right]=\frac{5}{2}\)

\(\Rightarrow\frac{x}{3}\left[1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{13}-\frac{1}{16}\right]=\frac{5}{2}\)

\(\Rightarrow\frac{x}{3}\left[1-\frac{1}{16}\right]=\frac{5}{2}\)

\(\Rightarrow\frac{x}{3}\cdot\frac{15}{16}=\frac{5}{2}\)

\(\Rightarrow\frac{x}{3}=\frac{5}{2}:\frac{15}{16}\)

\(\Rightarrow\frac{x}{3}=\frac{5}{2}\cdot\frac{16}{15}\)

\(\Rightarrow\frac{x}{3}=\frac{1}{1}\cdot\frac{8}{3}\)

\(\Rightarrow\frac{x}{3}=\frac{8}{3}\Leftrightarrow x=8\)

`-5/7xx3/13-5/7xx10/13+12/7`

`=-5/7xx(3/13+10/13)+12/7`

`=-5/7xx13/13+12/7=-5/7+12/7=7/7=1`

=-5/7x(3/13 + 10/13) +12/7
=-5/7x1+12/7
= -5/7+ 12/7
= 7/7 =1

= 1

cach lam thi ko nho nhung ket qua 100 % la 51/610

x=3/13

\(\dfrac{x+7}{13}=\dfrac{10}{13}\)

\(\Leftrightarrow13\left(x+7\right)=13.10\)

\(\Leftrightarrow13x+91=130\)

\(\Leftrightarrow13x=39\)

\(\Leftrightarrow x=3\)

\(\dfrac{x+7}{13}=\dfrac{10}{13}\Rightarrow\dfrac{x}{13}+\dfrac{7}{13}=\dfrac{10}{13}\Rightarrow\dfrac{x}{13}=\dfrac{3}{13}\Rightarrow x=3\)

ko quan tâm

sao ko quan tâm