c - d - a -b

Cảm ơn ạ

Bài 3: 

g: \(\left|x\right|< 2\)

nên -2<x<2

i: Ta có: \(\left|x-3\right|=x-3\)

\(\Leftrightarrow x-3\ge0\)

hay \(x\ge3\)

1)

a) 4y²-4xy+x²= x²-4xy+4y²= (x-2y)²

b) 9x²-12xy+4y²= (3x)²-2.3x.2y+(2y)²= (3x-2y)²

c) 16x²-25=(4x)²-5²= (4x-5)(4x+5)

d) 1-9y²= 1²-(3y)²=(1-3y)(1+3y)

g) x³-27y³= (x-3y)(x²+3xy+9y²)

h) 64 + 8x³=(4+2x)(16+8x+4x²)

1 c

1C

2 ko có đáp án đúng

3B

4A

5C

6D

7D

8B

Bài 5:

a: \(A=\frac{-3\left(x+1\right)}{x^2-x-6}\)

\(=\frac{-3\left(x+1\right)}{x^2-3x+2x-6}\)

\(=\frac{-3\left(x+1\right)}{\left(x-3\right)\left(x+2\right)}\)

\(x^2-4=0\)

=>(x-2)(x+2)=0

=>x=2(nhận) hoặc x=-2(loại)

Khi x=2 thì \(A=\frac{-3\cdot\left(2+1\right)}{\left(2-3\right)\left(2+2\right)}=\frac{-3\cdot3}{\left(-1\right)\cdot4}=\frac94\)

b: \(B=\frac{2x}{x+3}-\frac{x}{3-x}-\frac{3x^2+9}{x^2-9}\)

\(=\frac{2x}{x+3}+\frac{x}{x-3}-\frac{3x^2+9}{\left(x-3\right)\left(x+3\right)}\)

\(=\frac{2x\left(x-3\right)+x\left(x+3\right)-3x^2-9}{\left(x-3\right)\left(x+3\right)}=\frac{2x^2-6x+x^2+3x-3x^2-9}{\left(x-3\right)\left(x+3\right)}\)

\(=\frac{-3x-9}{\left(x-3\right)\left(x+3\right)}=\frac{-3\left(x+3\right)}{\left(x-3\right)\left(x+3\right)}=\frac{-3}{x-3}\)

c: P=B:A

\(=-\frac{3}{x-3}:\frac{-3\left(x+1\right)}{\left(x-3\right)\left(x+2\right)}\)

\(=\frac{3}{x-3}\cdot\frac{\left(x-3\right)\left(x+2\right)}{3\left(x+1\right)}=\frac{x+2}{x+1}\)

Để P nguyên thì x+2⋮x+1

=>x+1+1⋮x+1

=>1⋮x+1

=>x+1∈{1;-1}

=>x∈{0;-2}

mà x là số tự nhiên

nên x=0

Bài 3:

\(1,x=9\Leftrightarrow A=\dfrac{3-2}{9+3}=\dfrac{1}{12}\\ 2,P=AB=\dfrac{\sqrt{x}-2}{x+3}\cdot\dfrac{x-3\sqrt{x}+2-2+5\sqrt{x}}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+2\right)}\\ P=\dfrac{\sqrt{x}\left(\sqrt{x}+2\right)}{\left(x+3\right)\left(\sqrt{x}+2\right)}=\dfrac{\sqrt{x}}{x+3}\\ 3,\left(10x+30\right)P\ge x+25\\ \Leftrightarrow\dfrac{3\sqrt{x}\left(x+3\right)}{x+3}-x-25\ge0\\ \Leftrightarrow3\sqrt{x}-x-25\ge0\\ \Leftrightarrow-\left(x-3\sqrt{x}+\dfrac{9}{4}\right)-\dfrac{91}{4}\ge0\\ \Leftrightarrow-\left(\sqrt{x}-\dfrac{3}{2}\right)^2-\dfrac{91}{4}\ge0\left(vô.lí\right)\\ \Leftrightarrow x\in\varnothing\)

khuyến cáo ko nên gạt xuống.

Đồ ngu đồ ăn hại cút mịa mài đê :D