Đổ i \(2\begin{cases}3\\5\end{cases}\) m= 26dm

Sợi dây thứ 2 dài số m là : 26-19=7(dm) = 0,7m

                                             Đáp số 0,7m

cho mình hỏi 0,7m là gì, mình chưa học?

Giả sử \(\frac{a}{b}=\frac{c}{d}\)Suy ra  điều ta cần chứng minh là \(\frac{a+3c}{b+3d}=\frac{a+c}{b+d}\)

Theo tính chất của dãy tỉ số bằng nhau :

\(\hept{\begin{cases}\frac{a}{b}=\frac{c}{d}=\frac{a+c}{b+d}\\\frac{a}{b}=\frac{3c}{3d}=\frac{a+3c}{b+3d}\end{cases}}< =>\frac{a+3c}{b+3d}=\frac{a+c}{b+d}\)

Vậy ta có điều phải chứng minh

Ta có : \(\frac{a+3c}{b+3d}=\frac{a+c}{b+d}\)

=> (a + 3c)(b+ d) = (b + 3d)(a + c)

=> ab +ad + 3bc + 3cd = ab + bc + 3ad + 3cd

=> ad + 3bc  = bc + 3ad

=> 3bc - bc = 3ad - ad

=> 2bc = 2ad

=> bc = ad

=> \(\frac{a}{b}=\frac{c}{d}\) (đpcm)

Em ko chắc nhé 

a, \(\left|x-1\right|+\left|2-x\right|=3\)

\(\Leftrightarrow\left|x-1+2-x\right|=3\Leftrightarrow\left|1\right|\ne3\)

b, \(\left|x+3\right|+\left|x-5\right|=3x-1\)

\(\Leftrightarrow\left|x+3+x-5\right|=3x-1\)

\(\Leftrightarrow\left|2x-2\right|=3x-1\Leftrightarrow\orbr{\begin{cases}2x-2=3x-1\\-2x+2=3x-1\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}-x-1=0\\-5x+3=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-1\\x=\frac{3}{5}\end{cases}}}\)

a)  \(\left|x-1\right|+\left|2-x\right|=3\)

+) TH1 : \(\hept{\begin{cases}x-1\ge0\\2-x\ge0\end{cases}\Leftrightarrow\hept{\begin{cases}x\ge1\\x\le2\end{cases}\Leftrightarrow}1\le x\le2}\)

Ta có : \(\left|x-1\right|+\left|2-x\right|=3\)

\(\Leftrightarrow x-1+2-x=3\)

\(\Leftrightarrow1=3\)( vô lí ) 

+) TH2 : \(\hept{\begin{cases}x-1\le0\\2-x\le0\end{cases}\Rightarrow\hept{\begin{cases}x\le1\\x\ge2\end{cases}\left(L\right)}}\)

+) TH3 : \(\hept{\begin{cases}x-1\ge0\\2-x\le0\end{cases}\Rightarrow\hept{\begin{cases}x\ge1\\x\ge2\end{cases}\Leftrightarrow}x\ge2}\)

Ta có : \(\left|x-1\right|+\left|2-x\right|=3\)

\(\Leftrightarrow x-1+x-2=3\)

\(\Leftrightarrow2x-3=3\)

\(\Leftrightarrow x=3\)( Thỏa mãn ) 

+) TH4 : \(\hept{\begin{cases}x-1\le0\\2-x\ge0\end{cases}\Rightarrow\hept{\begin{cases}x\le1\\x\le2\end{cases}\Leftrightarrow}x\le1}\)

Ta có : \(\left|x-1\right|+\left|2-x\right|=3\)

\(\Leftrightarrow1-x+2-x=3\)

\(\Leftrightarrow3-2x=3\)

\(\Leftrightarrow x=0\) ( thỏa mãn ) 

Vậy tập nghiệm của phương trình là S = { 0 ; 3 }

P/s : ๖²⁴ʱ✰๖ۣۜCɦεɾɾү☠๖ۣۜBσмbʂ✰⁀ᶦᵈᵒᶫッ Ta có : \(\left|a\right|+\left|b\right|\ge\left|a+b\right|\). => Sai rùi nha bạn ^_^

\(x^3+x^2+4=0\)

\(\Leftrightarrow x^3+2x^2-x^2-2x+2x+4=0\)

\(\Leftrightarrow x^2\left(x+2\right)-x\left(x+2\right)+2\left(x+2\right)=0\)

\(\Leftrightarrow\left(x+2\right)\left(x^2-x+2\right)=0\)

\(\Leftrightarrow\left(x+2\right)\left(x^2-2.x.\frac{1}{2}+\frac{1}{4}+\frac{7}{4}\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x+2=0\\\left(x-\frac{1}{2}\right)^2+\frac{7}{4}>0\left(\forall x\right)\end{cases}}\)

\(\Leftrightarrow x=-2\)

Answer:

Let's go to the show to enjoy the show watching
I and my sister the Voice -  a  show on TV

a) Áp dụng định lí py-ta-go vào tam giác ABC , ta có :

\(BC^2=AB^2+AC^2\)

\(BC^2=3^2+4^2\)

\(\Leftrightarrow BC=\sqrt{9+16}=\sqrt{25}=5\left(cm\right)\)

b) Vì AM là đường trung tuyến 

Mà BC là cạnh huyền

=> AM = BM = CM 

MÀ AM = MD

=> AM = MD = BM = CM

<=> AM + MD = BM + MC

<=> AD = BC .

Xét tứ giác ABDC có : AD = BC và AD cắt BC tại trung điểm M của mỗi đường

=> ABDC là hình chữ nhật 

=> AB = CD ; AB // CD

If there is just one single thing more astonishing than the ability of the adult human being to talk, it is the process by which someone learns to do this. Some parts of the process are still (1)___quite_____ much a closed book, but it is for the (2)____visible_____ part possible to describe what the child is doing at various stages in its development, even if we cannot account (3)___for_____ how exactly it learns to do these things.

In fact, research carried out by various linguists has (4)___given______ rise to as many theories as there are differences in the rate of development. A baby actually makes sounds from the moment it is born, but for some time these are rather far removed (5)_____by____ arulate speech. In something a year, a baby will probably be at a stage where one or two syllables represent the peak of its achievement as a speaker; one more year and it will be (6)___better____ out with short phrases, and after this it seems (7)________ time at all before the child is capable of uttering complete sentences.

    Despite being a truly remarkable feat of learning, this is one that is performed by the vast (8)___diversity______ of human beings. Complex operations are brought (9)________ play in these dealing with speech and language; the key (10)_______ in brain work, though tongue – work and ear – work play a part in the whole process