\(\left(1900-2x\right):35-32=16\)

\(\left(1900-2x\right):35=48\)

\(1900-2x=1680\)

\(2x=220\)

\(x=110\)

\(\left(1900-2x\right):35=16+32\)

\(\left(1900-2x\right):35=48\)

\(1900-2x=48.35\)

\(1900-2x=1680\)

\(2x=1900-1680\)

\(2x=220\)

\(x=220:2\)

\(x=110\)

Vậy x=110

(1900-2x):35-32=16

(1900-2x):35=16+32

(1900-2x):35=48

1900-2x=48.35

1900-2x=1680

         2x=1900-1680 

         2x=220

           x=220:2

           x=110

(dấu "."là dấu nhân nha bạn)

a) \(A=\dfrac{1}{x+5}+\dfrac{2}{x-5}-\dfrac{2x+10}{\left(x+5\right)\left(x-5\right)}\)

\(A=\dfrac{x-5+2x+10-2x-10}{\left(x+5\right)\left(x-5\right)}=\dfrac{x-5}{\left(x+5\right)\left(x-5\right)}=\dfrac{1}{x+5}\)

b) \(A=-3\Rightarrow\dfrac{1}{x+5}=-3\)

\(\Leftrightarrow x+5=-\dfrac{1}{3}\Leftrightarrow x=-\dfrac{1}{3}-5=\dfrac{-16}{3}\)

\(9x^2-42x+49=\left(3x-7\right)^2=\left(3.\dfrac{-16}{3}-7\right)^2=\left(-23\right)^2=529\) \(\left(x=\dfrac{-16}{3}\right)\)

2x+6 chia hết cho x+1

=>2(x+1)+4 chia hết cho x + 1

=> 4 chia hết cho x + 1

=> x+1 thuộc Ư(4)={±1;±2;±4}

=> x thuộc {0;-2;1;-3;3;-5}

\(\hept{\begin{cases}2x=5y\\3x+4y=46\end{cases}}\Leftrightarrow\hept{\begin{cases}\frac{x}{\frac{1}{2}}=\frac{y}{\frac{1}{5}}\\3x+4y=46\end{cases}}\Leftrightarrow\hept{\begin{cases}\frac{3x}{\frac{3}{2}}=\frac{4y}{\frac{4}{5}}\\3x+4y=46\end{cases}}\)

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

\(\frac{3x}{\frac{3}{2}}=\frac{4y}{\frac{4}{5}}=\frac{3x+4y}{\frac{3}{2}+\frac{4}{5}}=\frac{46}{\frac{23}{10}}=20\)

\(\frac{3x}{\frac{3}{2}}=20\Rightarrow3x=30\Rightarrow x=10\)

\(\frac{4y}{\frac{4}{5}}=20\Rightarrow4y=16\Rightarrow y=4\)

2.x=5.y   = \(\frac{X}{5}\)=\(\frac{Y}{2}\)=\(\frac{3x+4Y}{3.5+4.2}\)=\(\frac{46}{23}\)=2

\(\frac{X}{5}\)=2 => x=2.5=10

\(\frac{Y}{2}\)=2 =>y=2.2=4

\(\frac{1.3.5+2.6.10+4.12.20+7.21.35}{1.5.7+2.10.14+4.20.28+7.35.49}\)

\(=\frac{1.3.5\left(1+2+4+7\right)}{1.5.7\left(1+2+7+7\right)}=\frac{1.3.5}{1.5.7}=\frac{15}{35}=\frac{3}{7}\)

\(\frac{1\cdot3\cdot5+2\cdot6\cdot10+4\cdot12\cdot20+7\cdot21\cdot35}{1\cdot5\cdot7+2\cdot10\cdot14+4\cdot20\cdot28+7\cdot35\cdot49}\)

\(=\)\(\frac{1\cdot3\cdot5\cdot\left(1+2+4+7\right)}{1\cdot5\cdot7\cdot\left(1+2+7+7\right)}\)

\(=\frac{1\cdot3\cdot5}{1\cdot5\cdot7}\)\(=\frac{15}{35}=\frac{3}{7}\)

bn vội quá viết nhầm lun kìa 

hj hj chúc bn làm bài tốt nha

b, x^3 = 243: 9

    x^3 = 27

    x =  3

Ta có : 3(2x - 1)² \(\ge0\forall x\)

           7(3y + 5)² \(\ge0\forall x\)

Mà : 3(2x - 1)² + 7(3y + 5)² = 0 

Nên : 3(2x - 1)² = 7(3y + 5)² = 0 

\(\Leftrightarrow\hept{\begin{cases}3\left(2x-1\right)^2=0\\7\left(3y+1\right)^2=0\end{cases}}\)

\(\Leftrightarrow\hept{\begin{cases}\left(2x-1\right)^2=0\\\left(3y+1\right)^2=0\end{cases}}\)

\(\Leftrightarrow\hept{\begin{cases}\left(2x-1\right)=0\\\left(3y+1\right)=0\end{cases}}\)

\(\Leftrightarrow\hept{\begin{cases}2x=1\\3y=-1\end{cases}}\)

\(\Leftrightarrow\hept{\begin{cases}x=\frac{1}{2}\\y=-\frac{1}{3}\end{cases}}\)

a, 1 + 3 + 5 + 7 + ............. + n 

=\(\frac{\left(n+1\right)\left(n-1\right)}{2}\)=676

=>\(\left(n+1\right)\left(n-1\right)\)=676*2 =1352

Còn lạ bạn tự suy luận là ra

[1+n].n:2=676

[1+n].n=1352=35.37

n=20

[2+n].n:2=992

[2+n].n=1984=42.44

n=44

Nè mình còn một câu nữa đấy ! Trả lời giùm mình câu đó đi nha !

a: A=2/9(9+99+...+99..99)

=2/9(10-1+10^2-1+...+10^22-1)

=2/9[10+10^2+...+10^22-22]

Đặt B=10+10^2+...+10^22

=>10B=10^2+10^3+...+10^23

=>B=(10^23-10)/9

=>\(A=\dfrac{2}{9}\cdot\left(\dfrac{10^{23}-10}{9}-22\right)\)

=>\(A=\dfrac{2\cdot10^{23}-416}{81}\)