\(1,\)

\(\left(x^2-9y^2\right)\left(4x+12y\right)\)

\(=\left(x-3y\right)\left(x+3y\right)-4\left(x+3y\right)\)

\(=\left(x+3y\right)\left(x-3y-4\right)\)

\(3,\)

\(-x^2+2xy-y^2+25\)

\(=-\left(x^2-2xy+y^2\right)+25\)

\(=25-\left(x-y\right)^2\)

\(=5^2-\left(x-y\right)^2\)

\(=\left(5-x+y\right)\left(5+x-y\right)\)

là sao k hiểu viết rõ ra đc k

Tìm x ,biết

a,/X/=1,7

b, 2 ./x/=5 và x<0 

1.I do => I did

2.do => did

3.goes => is going

4.are => \

1. Tìm lỗi :

1, What did you do last night ?I do my home work => did

2, What home do you get up yesterday morning ? => time

3, Where is your mother now ?She goes shopping => is going

4, Which class you are in  ? I'm in class 6B => are you

(10x + 2⁴) . 7⁴ = 2.7⁷

=> 10x + 16 = 2.7⁷ : 7⁴

=> 10x + 16 = 686

=> 10x = 686 - 16

=> 10x = 670

=> x = 67

cảm ơn Nhạt

72,5 - ( 2x + 1 ) = 630 : 9

72,5 - ( 2x + 1 ) = 70

2x + 1 = 72,5 - 70

2x + 1 = 2,5

2x = 2,5 - 1

2x = 1,5

x = 1,5 : 2

x = 0,75

72,5 - ( 2x + 1 ) = 630 : 9 

72,5 - ( 2x + 1 ) = 70 

           ( 2x + 1 ) = 72,5 - 70 

           ( 2x + 1 ) = 2,5

             2x         = 2,5 - 1 

             2x         = 1,5 

               x         = 1,5 : 2

              x          = 0,75 

Ta có : \(\hept{\begin{cases}\left|\frac{5}{6}x+\frac{7}{8}\right|\ge0\forall x\\\left(\frac{7}{12}:y-\frac{5}{6}\right)^2\ge0\forall y\end{cases}}\Leftrightarrow\hept{\begin{cases}2\left|\frac{5}{6}x+\frac{7}{8}\right|\ge0\\\frac{7}{2}\left(\frac{7}{12}:y-\frac{5}{6}\right)^2\ge0\end{cases}}\)

=> \(2\left|\frac{5}{6}x+\frac{7}{8}\right|+\frac{7}{2}\left(\frac{7}{12}:y-\frac{5}{6}\right)^2\ge0\)

Dấu "=" xảy ra <=> \(\hept{\begin{cases}\frac{5}{6}x+\frac{7}{8}=0\\\frac{7}{12}:y-\frac{5}{6}=0\end{cases}}\Leftrightarrow\hept{\begin{cases}x=-\frac{21}{20}\\y=\frac{7}{10}\end{cases}}\)

Vậy x = -21/20 ; y = 7/10 

a)x/27=-5/6

x=-5/6.27

x=-15

\(S=2\times4+4\times6+6\times8+...+18\times20\)

\(6\times S=2\times4\times6+4\times6\times\left(8-2\right)+6\times8\times\left(10-4\right)+...+18\times20\times\left(22-16\right)\)

\(=2\times4\times6+4\times6\times8-2\times4\times6+...+18\times20\times22-16\times18\times20\)

\(=18\times20\times22\)

\(\Rightarrow S=\frac{18\times20\times22}{6}=1320\)