Bài `5`
`a,(x-3)(x-2)-(x+1)(x-5)=0`
`<=>x^2 - 2x -3x+6 -(x^2 -5x+x-5)=0`
`<=>x^2-2x-3x+6-x^2+5x-x+5=0`
`<=> -x+11=0`
`<=> -x=-11`
`<=>x=11`
`b,(x+2)(x+3)-(x-2)(x+5)=0`
`<=>x^2+3x+2x+6 -(x^2 + 5x -2x-10)=0`
`<=>x^2+3x+2x+6-x^2-5x+2x+10=0`
`<=>2x+16=0`
`<=>2x=-16`
`<=> x= -8`
`c,(x-5)(-x+4)-(x-1)(x+3)=-2x^2`
`<=> -x^2 +4x+5x-20 -(x^2 + 3x-x-3)+2x^2=0`
`<=> -x^2 +4x+5x-20 -x^2 -3x+x+3+2x^2=0`
`<=>7x-17=0`
`<=> 7x=17`
`<=>x=17/7`
`d,3(2x-1)(3x-1)-(2x-3)(9x-1)=0`
`<=> (6x-3)(3x-1)-(18x^2 - 2x - 27x +3)=0`
`<=> 18x^2 -6x -9x+3-18x^2 +2x+27x-3=0`
`<=> 14x=0`
`<=>x=0`
`e,(12x-5)(4x-1)+(3x-7)(1-16x)=81`
`<=>48x^2 -12x-20x+5 + 3x- 48x^2 -7+112x+81=0`
`<=> 83x+79=0`
`<=> 83x=-79`
`<=>x=-79/83`
`2` câu tiếp theo làm tương tự nhé !
Bài `6`
`1,a,(6-x)^2`
`= 6^2 -2.6.x+x^2`
`= 36 - 12x+x^2`
`b,x^2-4`
`=x^2-2^2`
`=(x-2)(x+2)`
`c,(x-6)(6+x)`
`=(x-6)(x+6)`
`=x^2-6^2`
`=x^2-36`
`2,a,(x-5)^2`
`=x^2 -2.x.5 +5^2`
`=x^2 - 10x+25`
`b,1-4x^2`
`=1^2-(2x)^2`
`=(1-2x)(1+2x)`
`c,(2x+1)(2x-1)`
`=(2x)^2 -1^2`
`=4x^2-1`
`3,a,(5x+1)^2`
`= (5x)^2 + 2.5x.1+1^2`
`= 25x^2 + 10x+1`
`b,4x^2-9`
`=(2x)^2-3^2`
`= (2x-3)(2x+3)`
`c,(x-2y)(2y+x)`
`=(x-2y)(x+2y)`
`=x^2 - (2y)^2`
`=x^2-4y^2`
`4,a,(2x-1)^2`
`=(2x)^2 -2.2x.1+1^2`
`=4x^2 - 4x +1`
`b,9-25x^2`
`=3^2-(5x)^2`
`=(3-5x)(3+5x)`
`c,(3x-y^2)(3x+y^2)`
`= (3x)^2-(y^2)^2`
`= 6x^2-y^4`
`5,a,(2x+3)^2`
`=(2x)^2 + 2.2x.3 +3^2`
`= 4x^2 + 12x+9`
`b,4x^2-25`
`=(2x)^2 -5^2`
`=(2x-5)(2x+5)`
`c,(x^2-2y)(x^2+2y)`
`=(x^2)^2 - (2y)^2`
`= x^4 - 4y^2`
`6,(3+2x)^2`
`= 3^2+2.3.2x+(2x)^2`
`= 9 + 12x+4x^2`
`b,9x^2-36`
`=(3x)^2 - 6^2`
`=(3x-6)(3x+6)`
`c,(5x-3y)(3y+5x)`
`= (5x-3y)(5x+3y)`
`= (5x)^2 -(3y)^2`
`= 25x^2 - 9y^2`
Bài `7`
Bạn chỉ cần nhân ra rồi thực hiện phép tính như bài `5` nhé .
Bài `8`
`a,4x(x-2)-6+3x=0`
`<=> 4x(x-2) - (6-3x)=0`
`<=> 4x(x-2) - 3(2-x)=0`
`<=>4x(x-2) +3(x-2)=0`
`<=>(x-2)(4x+3)=0`
\(\Leftrightarrow\left[{}\begin{matrix}x-2=0\\4x+3=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=2\\x=-\dfrac{3}{4}\end{matrix}\right.\)
`a,x(x+2)-3(x+2)=0`
`<=>(x+2)(x-3)=0`
\(\Leftrightarrow\left[{}\begin{matrix}x+2=0\\x-3=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=-2\\x=3\end{matrix}\right.\)
`a,8x(x-5)-2x+10=0`
`<=>8x(x-5)-(2x-10)=0`
`<=> 8x(x-5) -2(x-5)=0`
`<=>(x-5)(8x-2)=0`
\(\Leftrightarrow\left[{}\begin{matrix}x-5=0\\8x-2=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=5\\x=\dfrac{2}{8}=\dfrac{1}{4}\end{matrix}\right.\)
`a,x(2x-3)-2(3-2x)=0`
`<=>x(2x-3)+2(2x-3)=0`
`<=>(2x-3)(x+2)=0`
\(\Leftrightarrow\left[{}\begin{matrix}2x-3=0\\x+2=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=-2\end{matrix}\right.\)
Mấy câu còn lại nhân ra giống bài `5`
8:
a: =>(x+1)(x-x+1)=0
=.x+1=0
=>x=-1
b: =>x^2+6x+9-x^2+4=4x+17
=>6x+13=4x+17
=>2x=4
=>x=2
c: =>(x-2)(4x+3)=0
=>x=-3/4 hoặc x=2
d: =>4x^2+4x+1-4x^2+12x-x+3-5=0
=>15x-1=0
=>x=1/15
