B=18=>A=9

\(1,=0,9\left|x\right|\\ 2,Sửa:\dfrac{\sqrt{63y^3}}{\sqrt{7y}}=\sqrt{\dfrac{63y^3}{7y}}=\sqrt{9y^2}=3\left|y\right|=-3y\)

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

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

\(= x 2 + 2 x y + y 2 + x 2 − 2 x y + y 2 − 2 x 2 = 2 y 2\)

\(2,=x^2-3^2=\left(x-3\right)\left(x+3\right)\\ 3,=\left(x+y-x+y\right)\left(x+y+x-y\right)\\ =2y\cdot2x=4xy\)

x^2-9=x^2-3^2=(x+3)(x-3)
(x+y)^2-(x-y)^2=(x+y+x-y)(x+y-x-y)=2x

x²-3²=(x-3)(x+3)

(x+y)²-(x-y)²=(x+y-x+y)(x+y+x-y)=2y⋅2x=4xy

4 - ( y +15)+32

4 -  y - 15 +32

4 - y  - 47

4 - 47 - y

(-43 ) - y

Lời giải:

$2-(y+20)+43=2-y-20+43=(43+2-20)-y=25-y$

\((4x+y)^2-(4x-y)^2\\=[(4x+y)-(4x-y)][(4x+y)+(4x-y)]\\=(4x+y-4x+y)(4x+y+4x-y)\\=2y\cdot8x\\=16xy\)

`C4:`

`x/[x-2]+2/[2-x]=x/[x-2]-2/[x-2]=[x-2]/[x-2]=1`

`C5:[15x^2]/[17y^4] . [34y^5]/[15x^3]`

 `=[15x^2 . 2.17y^4 . y]/[17y^4 . 15x^2 . x]=[2y]/x`

`C5:[6x+18]/[(x+4)^2]:[3(x+3)]/[x+4]`

 `=[6(x+3)]/[(x+4)^2] . [x+4]/[3(x+3)]`

`=2/[x+4]`