Chu vi : \(\left(4+2\right).2=12\left(m\right)\)

\(S=4.2=8\left(m^2\right)\)

giúp mình với

\(2\dfrac{2}{5}\times\dfrac{-3}{4}\)

\(=\dfrac{12}{5}\times\dfrac{-3}{4}\)

\(=-\dfrac{36}{20}\)

\(=-\dfrac{9}{5}\)

\(x^2⋮6\Rightarrow x^2\in\left\{1;2;3;6\right\}\)

\(\Rightarrow x\in\left\{1;\sqrt[]{2};\sqrt[]{3};\sqrt[]{6}\right\}\)

\(\Rightarrow x\in\left\{1\right\}\left(x\in N\right)\)

\(\Rightarrow\forall x\inℕ,x^2⋮6\Rightarrow x⋮6\) là mệnh đề sai

Bạn xem lại nhé, đề viết với mọi x ∈ N mà bạn, bạn mới xét vài trường hợp chứ không bao quát

Bài 2:

\(\dfrac{a+b}{a-b}=\dfrac{c+a}{c-a}\)

\(\Rightarrow\dfrac{a+b}{c+a}=\dfrac{a-b}{c-a}=\dfrac{a+b+a-b}{c+a+c-a}=\dfrac{a}{c}\) (T/c dãy tỷ số = nhau)

\(\Rightarrow\dfrac{a+b}{c+a}=\dfrac{a}{c}\Rightarrow c\left(a+b\right)=a\left(c+a\right)\)

\(\Rightarrow ac+bc=ac+a^2\Rightarrow a^2=bc\)

a) x=949/27
    y=755/27
    z=61/9
    các bạn xem giúp mik đúng chx ạ, mik đặt là k

nhanh lên mn ơi tớ đang cần gấp :v

Đề thiếu rồi

\(\left|5x-3\right|-x=7\\ \Leftrightarrow\left|5x-3\right|=7+x\)

Nếu \(\left\{{}\begin{matrix}5x-3\ge0\Leftrightarrow5x\ge3\Leftrightarrow x\ge\dfrac{3}{5}\\5x-3< 0\Leftrightarrow5x< 3\Leftrightarrow x< \dfrac{3}{5}\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}5x-3=7+x\\-\left(5x-3\right)=7+x\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}5x-x=7+3\\-5x+3=7+x\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}4x=10\\-5x-x=7-3\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=\dfrac{10}{4}\\-6x=4\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=\dfrac{5}{2}\left(tm\right)\\x=-\dfrac{2}{3}\left(tm\right)\end{matrix}\right.\)

Đề là gì cậu?

A = \(\dfrac{3}{1-2x}\) ( A \(\in\) Z; \(x\in\) Z)

A \(\in\) Z ⇔ 3 ⋮ 1 - 2\(x\) 

Ư(3) = { -3; -1; 1; 3}

lập bảng ta có: 

Theo bảng trên ta có: \(x\in\) { -1; 0; 1; 2}

a) \(\dfrac{x}{2}=\dfrac{y}{5}=\dfrac{z}{7};x+y+z=56\)

\(\dfrac{x}{2}=\dfrac{y}{5}=\dfrac{z}{7}=\dfrac{x+y+z}{2+5+7}=\dfrac{56}{14}=4\)

\(\Rightarrow\left\{{}\begin{matrix}x=4.2=8\\y=4.5=20\\z=4.7=28\end{matrix}\right.\)

b) \(\dfrac{x}{1,1}=\dfrac{y}{1,3}=\dfrac{z}{1,4}\left(1\right);2x-y=5,5\)

\(\left(1\right)\Rightarrow\dfrac{2x-y}{1,1.2-1,3}=\dfrac{5,5}{0,9}\)

\(\Rightarrow\left\{{}\begin{matrix}x=1,1.\dfrac{5,5}{0,9}=\dfrac{6,05}{0,9}\\y=1,3.\dfrac{5,5}{0,9}=\dfrac{7,15}{0,9}\\z=\dfrac{1,4}{1,1}.x=\dfrac{1,4}{1,1}.\dfrac{6,05}{0,9}=\dfrac{8,47}{0,99}\end{matrix}\right.\)

d) \(\dfrac{x}{2}=\dfrac{x}{3}=\dfrac{z}{5};xyz=-30\)

\(\dfrac{x}{2}=\dfrac{x}{3}=\dfrac{z}{5}=\dfrac{xyz}{2.3.5}=\dfrac{-30}{30}=-1\)

\(\Rightarrow\left\{{}\begin{matrix}x=2.\left(-1\right)=-2\\y=3.\left(-1\right)=-3\\z=5.\left(-1\right)=-5\end{matrix}\right.\)

a) �2=�5=�7;�+�+�=562x​=5y​=7z​;x+y+z=56

�2=�5=�7=�+�+�2+5+7=5614=42x​=5y​=7z​=2+5+7x+y+z​=1456​=4

⇒{�=4.2=8�=4.5=20�=4.7=28⇒⎩⎨⎧​x=4.2=8y=4.5=20z=4.7=28​

b) �1,1=�1,3=�1,4(1);2�−�=5,51,1x​=1,3y​=1,4z​(1);2x−y=5,5

(1)⇒2�−�1,1.2−1,3=5,50,9(1)⇒1,1.2−1,32x−y​=0,95,5​
    

⇒⎩⎨⎧​x=1,1.0,95,5​=0,96,05​y=1,3.0,95,5​=0,97,15​z=1,11,4​.x=1,11,4​.0,96,05​=0,998,47​​

d) �2=�3=�5;���=−302x​=3x​=5z​;xyz=−30

�2=�3=�5=���2.3.5=−3030=−12x​=3x​=5z​=2.3.5xyz​=30−30​=−1

⇒{�=2.(−1)=−2�=3.(−1)=−3�=5.(−1)=−5⇒⎩⎨⎧​x=2.(−1)=−2y=3.(−1)=−3z=5.(−1)=−5​
 

a) 9x-1/4=3/2

=>9x=3/2+1/4

=>9x=7/4

=>x=7/4:9

=>x=7/36

Vậy x=7/36

b)(4x+2):2,5=3,2:0,5

=>(4x+2):2,5=6,4

=>4x+2=6,4.2,5

=>4x+2=16

=>4x=16-2

=>4x=14

=>x=14:4

=>x=7/2

Vậy x=7/2

c) 5,4/x-2=6/7

=>5,4/x=6/7+2

=>5,4/x=20/7

=>x=5,4 :20/7

=>x=1,89

Vậy x= 1,89

d) 0,5:2=3:(2x+7)

=>3:(2x+7)=0,25

=>2x+7=3:0,25

=>2x+7=12

=>2x=12-7

=>2x=5

=>x=5/2

Vậy x=5/2

a) 9x-1/4=3/2

=>9x=3/2+1/4

=>9x=7/4

=>x=7/4:9

=>x=7/36

Vậy x=7/36

b)(4x+2):2,5=3,2:0,5

=>(4x+2):2,5=6,4

=>4x+2=6,4.2,5

=>4x+2=16

=>4x=16-2

=>4x=14

=>x=14:4

=>x=7/2

Vậy x=7/2

c) 5,4/x-2=6/7

=>5,4/x=6/7+2

=>5,4/x=20/7

=>x=5,4 :20/7

=>x=1,89

Vậy x= 1,89

d) 0,5:2=3:(2x+7)

=>3:(2x+7)=0,25

=>2x+7=3:0,25

=>2x+7=12

=>2x=12-7

=>2x=5

=>x=5/2

Vậy x=5/2

\(...=\dfrac{5}{2}+\dfrac{6}{9}=\dfrac{5}{2}+\dfrac{2}{3}=\dfrac{15}{6}+\dfrac{4}{6}=\dfrac{19}{6}\)