hai góc kề bù => AOB + BOC = 180⁰

                      => 70⁰ + BOC = 180 ⁰

                           => BOC = 110⁰

2³.4²: 8² = 2.(2².4²): 8² = 2.8² : 8² = 2 

giúp vs ạ

\(-3\dfrac{1}{7}.\dfrac{6}{55}.\dfrac{-7}{12}\)

`=-22/7 . 6/55 . (-7)/12`

`=(-22.6.(-7))/(7.55.12)`

`=`\(\dfrac{-2.1.\left(-1\right)}{1.5.2}\)

`=2/10`

`=1/5`

Lời giải:
a. $\frac{a}{b}=\frac{3}{4}\Rightarrow \frac{a}{3}=\frac{b}{4}$

Đặt $\frac{a}{3}=\frac{b}{4}=k\Rightarrow a=3k; b=4k$ 

Khi đó:
$B=\frac{2a-5b}{a-3b}=\frac{2.3k-5.4k}{3k-3.4k}=\frac{-14k}{-9k}=\frac{14}{9}$

b.

$a-b=7\Rightarrow b=a-7$. Khi đó:
$C=\frac{3a-b}{2a+7}+\frac{3b-a}{2b-7}=\frac{3a-(a-7)}{2a+7}+\frac{2b+a-7-a}{2b-7}$
$=\frac{2a+7}{2a+7}+\frac{2b-7}{2b-7}=1+1=2$

Lời giải:
a. $(3x-\frac{1}{5})^3=\frac{64}{125}=(\frac{4}{5})^3$

$3x-\frac{1}{5}=\frac{4}{5}$

$3x=\frac{4}{5}+\frac{1}{5}=1$

$x=\frac{1}{3}$

b/

$(2x+\frac{3}{7})^2=\frac{100}{49}=(\frac{10}{7})^2=(\frac{-10}{7})^2$

$\Rightarrow 2x+\frac{3}{7}=\frac{10}{7}$ hoặc $2x+\frac{3}{7}=\frac{-10}{7}$

$\Rightarrow x=\frac{1}{2}$ hoặc $x=\frac{-13}{14}$

c.

$(x+\frac{2}{9})^5=(x+\frac{2}{9})^3$

$(x+\frac{2}{9})^5-(x+\frac{2}{9})^3=0$

$(x+\frac{2}{9})^3[(x+\frac{2}{9})^2-1]=0$

$\Rightarrow (x+\frac{2}{9})^3=0$ hoặc $(x+\frac{2}{9})^2=1$

Nếu $(x+\frac{2}{9})^3=0\Leftrightarrow x=\frac{-2}{9}$

Nếu $(x+\frac{2}{9})^2=1=1^2=(-1)^2$

$\Rightarrow x+\frac{2}{9}=1$ hoặc $x+\frac{2}{9}=-1$

$\Rightarrow x=\frac{7}{9}$ hoặc $x=\frac{-11}{9}$

bỏ chữ `d)` ra nhé

các bạn giúp mình được không ạ??

các pạn giúp mk nhanh dc ko.

gọi số bút công mua là x đk x >0

theo bài ra ta có ( x - 8): 3 = x -16⇔

                              x-8 = 3x - 48

                     ⇔ 3x - x =  48 - 8

                         ⇔ 2x =   40

                             x = 40 : 2

                           x = 20

tất cả số bút công mua có giá là 3500 x 20 = 70000(đồng)

đs....

`@`\(\dfrac{13}{4}+4x=\dfrac{7}{9}\)

`=>4x=-89/36`

`=>x=-89/144`

`@`\(\dfrac{5}{3}.\left(x-1\right)^3=\left(-2\right)^3\)

`=>5/3 .(x-1)^3=-8`

`=>(x-1)^3=-24/5`

\(\Rightarrow x-1=\sqrt[3]{-\dfrac{24}{5}}\)

\(\Rightarrow x=\sqrt[3]{-\dfrac{24}{5}}+1\)

`@`\(\left|2x+1\right|-1^2=3^2\)

\(\Rightarrow\left|2x+1\right|=10\)

\(\Rightarrow\left[{}\begin{matrix}2x+1=10\\2x+1=-10\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}x=\dfrac{9}{2}\\x=-\dfrac{11}{2}\end{matrix}\right.\)

\(0,5x+\dfrac{1}{3}-\dfrac{2}{3}\left(x+1\right)=\dfrac{2}{9}\)

\(\dfrac{1}{2}x+\dfrac{1}{3}-\dfrac{2}{3}x-\dfrac{2}{3}=\dfrac{2}{9}\)

\(\dfrac{-1}{6}x-\dfrac{1}{3}=\dfrac{2}{9}\)

\(\dfrac{-1}{6}x=\dfrac{5}{9}\)

\(x=\dfrac{5}{9}:\dfrac{-1}{6}\)

\(x=-\dfrac{10}{3}\)