`a, 8x=64`

`=>x= 64:8`

`=> x=8`

`b, (-5)x=25`

`=>x=25:(-5)`

`=>x=-5`

`c,4x+1=21`

`=>4x=21-1`

`=>4x=20`

`=>x=20:4`

`=>x=5`

`d, (-3)x-1=8`

`=>(-3)x=8+1`

`=>(-3)x=9`

`=>x=9:(-3)`

`=>x=(-3)`

Đây là câu hỏi mang lời chúc các bạn thi tốt, ở đây các bạn cũng được chia sẻ và gửi lời chúc đến mọi người. Câu hỏi không mang tính chất spam nên cũng không nhất thiết phải xóa đâu ⚡

`105-(115-3x)=30`

`=> 115-3x= 105-30`

`=>  115-3x= 75`

`=> 3x=115-75`

`=> 3x=40`

`=> x= 40/3`

D

C

Bài `1`

`a, (x+2)^2 =x^2 +4x+4`

`b, (x-5)^2=x^2 -10x+25`

`c,(2x-y)^2=(2x)^2- 2*2x*y+y^2=4x^2-4xy+y^2`

`d,(3x^2-2y)^2= (3x^2)^2 - 2*3x^2*2y +(2y)^2=9x^4-12x^2y +4y^2`

`e,,(2x-y)(4x^2+2xy+y^2)= (2x)^3-y^3=8x^3-y^3`

`f,(x+3)(x^2-3x+9)=x^3+3^3=x^3+27`

Bài `2`

\(a,4xy+4xz\\ =4x\left(y+z\right)\\ b,x^2-y^2+9-6x\\ =\left(x^2-6x+9\right)-y^2\\ =\left(x-3\right)^2-y^2\\ =\left(x-3-y\right)\left(x-3+y\right)\)

Bài `3`

\(a,\dfrac{3xy}{y+z}+\dfrac{3xz}{y+z}\\ =\dfrac{3xy+3xz}{y+z}\\ =\dfrac{3x\left(y+z\right)}{y+z}\\ =3x\\ b,\dfrac{x}{x+2}-\dfrac{x}{x-2}\\ =\dfrac{x\left(x-2\right)}{\left(x-2\right)\left(x+2\right)}-\dfrac{x\left(x+2\right)}{\left(x-2\right)\left(x+2\right)}\\ =\dfrac{x^2-2x-\left(x^2+2x\right)}{\left(x-2\right)\left(x+2\right)}\\ =\dfrac{x^2-2x-x^2-2x}{\left(x-2\right)\left(x+2\right)}\\ =\dfrac{-4x}{x-4}\)

`(x-1/2)^2 +(2x-1)^2=0`

\(\Rightarrow\left(x^2-x+\dfrac{1}{4}\right)+\left(4x^2-4x+1\right)=0\\ \Rightarrow x^2-x+\dfrac{1}{4}+4x^2-4x+1=0\\ \Rightarrow5x^2-5x+\dfrac{5}{4}=0\\ \Rightarrow\dfrac{5}{4}\left(4x^2-4x+1\right)=0\\ \Rightarrow\dfrac{5}{4}\left(2x-1\right)^2=0\\ \Rightarrow\left(2x-1\right)^2=0\\ \Rightarrow2x-1=0\\ \Rightarrow2x=0+1\\ \Rightarrow2x=1\\ \Rightarrow x=\dfrac{1}{2}\)

Ta có : `x^2+2xy+y^2=(x+y)^2`

Tại `x=4;y=3` ta có : `(x+y)^2 =(4+3)^2=7^2=49`

\(\left(\sqrt{12}+\sqrt{27}-\sqrt{18}\right)\cdot3\\ =(\sqrt{4\cdot3}+\sqrt{9\cdot3}-\sqrt{6}\cdot\sqrt{3})\cdot\sqrt{3}\\ =\left(2\sqrt{3}+3\sqrt{3}-\sqrt{6}\cdot\sqrt{3}\right)\cdot\sqrt{3}\\ =2\cdot3+3\cdot3-\sqrt{6}\cdot3\\ =6+9-3\sqrt{6}\\ =15-3\sqrt{6}\)

\(\left(15\sqrt{20}-3\sqrt{45}+2\sqrt{5}\right):\sqrt{5}\\ =\left(15\sqrt{4\cdot5}-3\sqrt{9\cdot5}+2\sqrt{5}\right):\sqrt{5}\\ =\left(30\sqrt{5}-9\sqrt{5}+2\sqrt{5}\right):\sqrt{5}\\ =30-9+2\\ =23\)