2x-138 = 8.9

2x - 138 = 72

2x = 138 + 72

2x = 210

x = 210 : 2

x = 105

\(2x-138=8.9\)

\(2x-138=72\)

\(2x=72+138\)

\(2x=210\)

\(x=105\)

2x-138=8.9

2x-138=72

2x = 72 + 138

2x = 210

x = 210 : 2

x = 105

a.70 -5.(x-3)=45

x-3=70-5-45

x-3=20

x=20-3=17

b.2x-138=8.9

2x-138=72

2x=72+138

2x=210

x=210:2=105

c.10+2n=16

2n=16-10

2n=6

n=6:3=2

d.[(4x+28).3+55]:5=35

[(4x+28).3+55]=35x5=175

4x+28=(175-55):3

4x+28=40

4x=40-28=12

x=12:4=3

Dung thi k mk nha

Chuc bn hoc gioi nha

𝑥=−54.5

G=\(\frac{8.9+8.9.10+8.9+11+8.9+2}{4.6+4.6.6+4.6.4+4.6.8}\)

G=\(\frac{8.9.\left(1+10+1+1\right)+11+2}{4.6.\left(1+6+4+8\right)}\)

G=\(\frac{72.13+13}{24.19}\)

G=\(\frac{13.\left(72+1\right)}{24.19}=\frac{13.73}{24.19}\)

G=\(\frac{949}{456}\)

Ta có: \(\left(\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+...+\dfrac{1}{8\cdot9}+\dfrac{1}{9\cdot10}\right)\cdot100-\left[\dfrac{5}{2}:\left(x+\dfrac{206}{100}\right)\right]:\dfrac{1}{2}=89\)

\(\Leftrightarrow100\left(\dfrac{1}{1}-\dfrac{1}{10}\right)-\left[\dfrac{5}{2}:\left(x+\dfrac{103}{50}\right)\right]\cdot2=89\)

\(\Leftrightarrow\dfrac{5}{2}:\left(x+\dfrac{103}{50}\right)=\dfrac{1}{2}\)

\(\Leftrightarrow x+\dfrac{103}{50}=5\)

hay \(x=\dfrac{147}{50}\)

\(5\times4\times2\times25\)

\(=\left(5\times2\right)\times\left(4\times25\right)\)

\(=10\times100=1000\)

________

\(138\times8+2\times138\)

\(=138\times\left(8+2\right)\)

\(=138\times10=1380\)

Bài3: Tính bằng cách thuận tiện nhất: 72,34×6,75+27,66×6,75=?

>_<

\(\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+....+\frac{1}{8.9}+\frac{1}{9.10}\right)\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-........-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\)

\(=1-\frac{1}{10}\)

\(=\frac{10}{10}-\frac{1}{10}=\frac{9}{10}\)

\(\Leftrightarrow\frac{9}{10}.100-\left[\frac{5}{2}:\left(x+\frac{206}{100}\right):\frac{1}{2}\right]=89\)

\(\Leftrightarrow90-\left[\frac{5}{2}:\left(x+\frac{206}{100}\right):\frac{1}{2}\right]=89\)

\(\Leftrightarrow\frac{5}{2}:\left(x+\frac{206}{100}\right):\frac{1}{2}=90-89=1\)

\(\Leftrightarrow\frac{5}{2}:\left(x+\frac{206}{100}\right)=1.\frac{1}{2}=\frac{1}{2}\)

\(\Leftrightarrow x+\frac{206}{100}=\frac{5}{2}:\frac{1}{2}\)

\(\Leftrightarrow x+\frac{103}{50}=\frac{5}{2}.2\)

\(\Leftrightarrow x+\frac{103}{50}=5\)

\(\Leftrightarrow x=5-\frac{103}{50}\)

\(\Leftrightarrow x=\frac{250}{50}-\frac{103}{50}\)

\(\Leftrightarrow x=\frac{147}{50}\)

Đặt \(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{8.9}+\frac{1}{9.10}\)

\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\)

\(A=1-\frac{1}{10}=\frac{9}{10}\)

\(\Rightarrow\frac{9}{10}.100-\left[\frac{5}{2}:\left(x+\frac{206}{100}\right)\right]:\frac{1}{2}=89\)

\(\Leftrightarrow90-\left[\frac{5}{2}:\left(x+\frac{206}{100}\right)\right]:\frac{1}{2}=89\)

\(\Rightarrow\frac{5}{2}:\left(x+\frac{206}{100}\right):\frac{1}{2}=90-89=1\)

\(\Leftrightarrow x+\frac{206}{100}=\frac{5}{2}:\frac{1}{2}:1=5\)

\(\Rightarrow x=5-\frac{206}{100}=\frac{147}{50}\)

Vậy \(x=\frac{147}{50}.\)