mình ko chép đề bài nha

a) \(\dfrac{16}{5}\): \(\dfrac{7}{3}\) : y =\(\dfrac{12}{7}\)

    \(\dfrac{48}{35}\): y        = \(\dfrac{12}{7}\)

           y        = \(\dfrac{48}{35}\): \(\dfrac{12}{7}\)

           y        = \(\dfrac{4}{5}\)

a) y = 5/4

b) y = 21

c) y = 41/12

b) 3 : y x \(\dfrac{7}{2}\)= \(\dfrac{1}{2}\)

    3 : y       = \(\dfrac{1}{2}:\dfrac{7}{2}\)

    3 : y       = \(\dfrac{1}{7}\)

         y       = 3 : \(\dfrac{1}{7}\)

         y       = 21

bài 1 : a,ta có 3/x-1 =4/y-2=5/z-3 =>  x-1/3=y-2/4=z-3/5 

áp dụng .... => x-1+y-2+z-3 / 3+4+5 = x+y+z-1-2-3/3+4+5 = 12/12=1

do x-1/3 = 1 => x-1 = 3 => x= 4 ( tìm y,z tương tự

Bài 1: 

a) Ta có: 3/x - 1 = 4/y - 2 = 5/z - 3 => x - 1/3 = y - 2/4 = z - 3/5 áp dụng ... =>x - 1 + y - 2 + z - 3/3 + 4 + 5 = x + y + z - 1 - 2 - 3/3 + 4 + 5 = 12/12 = 1 do x - 1/3 = 1 => x - 1 = 3 => x = 4 ( tìm y, z tương tự )

cũng dễ thôi

\(a,\Leftrightarrow y^3-6y^2+12y-8-y^3+27+6y^2+12y+6=49\\ \Leftrightarrow24y=24\Leftrightarrow y=1\\ b,\Leftrightarrow y^3+9y^2+27y+27-y^3-3y^2-3y-1=56\\ \Leftrightarrow6y^2+24y-30=0\\ \Leftrightarrow y^2+4y-5=0\\ \Leftrightarrow\left(y-1\right)\left(y+5\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}y=1\\y=-5\end{matrix}\right.\)

a) \(\Leftrightarrow y^3-6y^2+12y-8-y^3+27+6y^2+12y+6=49\)

\(\Leftrightarrow24y=24\Leftrightarrow y=1\)

b) \(\Leftrightarrow y^3+9y^2+27y+27-y^3-3y^2-3y-1=56\)

\(\Leftrightarrow6y^2+24y-30=0\)

\(\Leftrightarrow6\left(y-1\right)\left(y+5\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}y=1\\y=-5\end{matrix}\right.\)

a) (y-2)³-(y-3)(y²+3y+9)+6(y+1)²=49
    \(y^3-6y^2+12y-8-y^3+27+6\left(y^2+2y+1\right)=49\)
    \(-6y^2+12y+25+6y^2+12y+6=49\)
     \(24y+31=49\)
     24y=18
         y=0,75

\(A=3x^2y^3-5x^2+3x^3y^2\)

bậc 5, hệ số 3 

bạn xem lại đề B nhé 

A=15x²y²+7x²-8x³y²-12x²+11x³y²-12x²y²

A= (15x²y²-12x²y²)+(7x²-12x²)+(-8x³y²+11x³y²)

A= 3x²y²-5x²+3x³y²

Bậc là: 5

Hệ số cao nhất: 3

\(B=3x^5y+\left(\dfrac{-1}{3}\right)xy^4+34x^2y^3-\dfrac{1}{2}x^5y+2xy^4-x^2y^3\\ B=\dfrac{5}{2}x^5y+\dfrac{7}{3}xy^4-\dfrac{1}{4}x^2y^3\)

bậc là:6

hệ số cao nhất là:\(\dfrac{7}{3}\)

A=2y^3

Bậc là 3

Khi y=1/2 thì A=2*1/8=1/4

`a)TXĐ: R`

`b)TXĐ: R\\{0}`

`c)TXĐ: R\\{1}`

`d)TXĐ: (-oo;-1)uu(1;+oo)`

`e)TXĐ: (-oo;-1/2)uu(1/2;+oo)`

`f)TXĐ: (-oo;-\sqrt{2})uu(\sqrt{2};+oo)`

`h)TXĐ: (-oo;0) uu(2;+oo)`

`k)TXĐ: R\\{1/2}`

`l)ĐK: {(x^2-1 > 0),(x-2 > 0),(x-1 ne 0):}`

`<=>{([(x > 1),(x < -1):}),(x > 2),(x ne 1):}`

`<=>x > 2`

   `=>TXĐ: (2;+oo)`