4a = 5b 

\(\Rightarrow\dfrac{a}{5}=\dfrac{b}{4}\)

\(\Rightarrow\dfrac{2a}{10}=\dfrac{b}{4}\)

Áp dụng tính chất của dãy tỉ số bằng nhau , ta có :

\(\dfrac{2a}{10}=\dfrac{b}{4}=\dfrac{b-2a}{4-10}=\dfrac{-5}{-6}=\dfrac{5}{6}\)

\(\Rightarrow\left\{{}\begin{matrix}2a=\dfrac{5}{6}.10\\b=\dfrac{5}{6}.4\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}a=\dfrac{25}{6}\\b=\dfrac{10}{3}\end{matrix}\right.\)

\(A=\dfrac{1}{3}-0,25+0,2\)

\(A=\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{5}\)

\(A=\dfrac{20}{60}-\dfrac{15}{60}+\dfrac{12}{60}\)

\(A=\dfrac{17}{60}\)

TL: gọi n là tử số của số cần tìm, ta có:

\(\dfrac{-3}{8}\)<\(\dfrac{n}{7}\)<\(\dfrac{-1}{8}\)

=> -21<8n<-7

=> n=-2 hoặc  n=-1

=> Ta tìm được 2 phân số thỏa y/c là: \(\dfrac{-2}{7}\)và \(\dfrac{-1}{7}\)

a, \(\widehat{BOD}=180^o-60^o=120^o\)

Kể cả không vẽ thêm tai phân giác thì theo tính chất tia phân giác của 2 góc kề bề ta có thể biết nó có số đo độ là 90^o

giúp mình với

Bài làm: 

27⁵ : 81³ = 27

10⁶ : 100 = 10000

5⁹ : 25³ = 125

4¹⁰ : 64³ = 4

2²⁵ : 32⁴ = 32

học tốt#

\(27^5:81^3=\left(3^3\right)^5:\left(3^4\right)^3=3^{15}:3^{12}=3^{\left(15-12\right)}=3^3=27\)

\(10^6:100=10^6:10^2=10^{\left(6-2\right)}=10^4=10000\)

\(5^9:25^3=5^9:\left(5^2\right)^3=5^9:5^6=5^{\left(9-6\right)}=5^3=125\)

\(4^{10}:64^3=\left(2^2\right)^{10}:\left(2^6\right)^3=2^{20}:2^{18}=2^{\left(20-18\right)}=2^2=4\)

\(2^{25}:32^4=2^{25}:\left(2^5\right)^4=2^{25}:2^{20}=2^{\left(25-20\right)}=2^5=32\)

\((x-\dfrac{2}{9})^3=(\dfrac{2}{3})^6\)

\(=>(x-\dfrac{2}{9})^3=[(\dfrac{2}{3})^2]^3\)

\(=>(x-\dfrac{2}{9})^3=(\dfrac{4}{9})^3\)

\(=>x-\dfrac{2}{9}=\dfrac{4}{9}\)

\(=>x=\dfrac{4}{9}+\dfrac{2}{9}=\dfrac{2}{3}\)

(x - 2/9)3 = (2/3)6

(x - 2/9)3 = [(2/3²)]³

(x - 2/9)3 = (4/9)³

x - 2/9     = 4/9

x             = 4/9 + 2/9 

x             = 6/9 

x             = 2/3

Vậy x = 2/3 

7^{3 .} 4³ 

= ( 7.4 )³

= 28³

178 : 175

= 17⁸⁺⁵

= 17¹³

\(\left|x-\dfrac{1}{3}\right|+\dfrac{2}{3}=2\dfrac{1}{2}\)

\(\Leftrightarrow\left|x-\dfrac{1}{3}\right|+\dfrac{2}{3}=\dfrac{5}{2}\)

\(\Leftrightarrow\left|x-\dfrac{1}{3}\right|=\dfrac{5}{2}-\dfrac{2}{3}\)

\(\Leftrightarrow\left|x-\dfrac{1}{3}\right|=\dfrac{11}{6}\)

\(\Leftrightarrow\left[{}\begin{matrix}x-\dfrac{1}{3}=\dfrac{-11}{6}\\x-\dfrac{1}{3}=\dfrac{11}{6}\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{-11}{6}+\dfrac{1}{3}\\x=\dfrac{11}{6}+\dfrac{1}{3}\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{3}{2}\\x=\dfrac{13}{6}\end{matrix}\right.\)

\(|x-\dfrac{1}{3}|+\dfrac{2}{3}=2\dfrac{1}{2}\)

\(=>|x-\dfrac{1}{3}|+\dfrac{2}{3}=\dfrac{5}{2}\)

\(=>|x-\dfrac{1}{3}|=\dfrac{5}{2}-\dfrac{2}{3}=\dfrac{11}{6}\)

\(=>\) $\left[\begin{matrix} x-\dfrac{1}{3}=\dfrac{11}{6}\\ x-\dfrac{1}{3}=\dfrac{-11}{6}\end{matrix}\right.$

`=>` $\left[\begin{matrix} x=\dfrac{13}{6}\\ x=\dfrac{-3}{2}\end{matrix}\right.$