c: ta có: \(7x^2-2x-5=0\)

\(\Leftrightarrow\left(x-1\right)\left(7x+5\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-\dfrac{5}{7}\end{matrix}\right.\)

a: \(\Leftrightarrow\left(x+12-3x\right)\left(x+12+3x\right)=0\)

=>(-2x+12)(4x+12)=0

=>x=-3 hoặc x=6

b: \(\Leftrightarrow20x^3-15x^2+45x-45=0\)

=>\(x\simeq0.93\)

d: =>-4x+28+11x=-x+3x+15

=>7x+28=2x+15

=>5x=-13

=>x=-13/5

e: \(\Leftrightarrow4x^3-12x+x=4x^3-3x+5\)

=>-9x=-3x+5

=>-6x=5

=>x=-5/6

Bài 1:

a) \(9\left(4x+3\right)^2=16\left(3x-5\right)^2\)

\(114x^2+216x+81=114x^2-480x+400\)

\(144x^2+216x=144x^2-480x+400-81\)

\(114x^2+216=114x^2-480x+319\)

\(696x=319\)

\(\Rightarrow x=\frac{11}{24}\)

b) \(\left(x^3-x^2\right)^2-4x^2+8x-4=0\)

\(\left(x-1\right)^2\left(x^2+2\right)\left(x+\sqrt{2}\right)\left(x-\sqrt{2}\right)=0\)

\(\Rightarrow x=1\)

c) \(x^5+x^4+x^3+x^2+x+1=0\)

\(\left(x+1\right)\left(x^2+x+1\right)\left(x^2-x+1\right)=0\)

\(\Rightarrow x=-1\)

Bài 2:

a) \(5x^3-7x^2-15x+21=0\)

\(\left(5x-7\right)\left(x+\sqrt{3}\right)\left(x-\sqrt{3}\right)=0\)

\(\Rightarrow x=\frac{7}{5}\)

b) \(\left(x-3\right)^2=4x^2-20x+25\)

\(x^2-6x+9-25=4x^2-20x+25\)

\(x^2-6x+9=4x^2-20x+25-25\)

\(x^2-6x-16=4x^2-20x\)

\(x^2+14x-16=4x^2-4x^2\)

\(-3x^2+14x-16=0\)

\(\Rightarrow\orbr{\begin{cases}x=2\\x=\frac{8}{3}\end{cases}}\)

c) \(\left(x-1\right)^2-5=\left(x+2\right)\left(x-2\right)-x\left(x-1\right)\)

\(x^2-2x=x-4\)

\(x^2-2x=x-4+4\)

\(x^2-2x=x-x\)

\(x^2-3x=0\)

\(\Rightarrow\orbr{\begin{cases}x=0\\x=3\end{cases}}\)

d) \(\left(2x-3\right)^3-\left(2x+3\right)\left(4x^2-1\right)=-24\)

\(-48x^2+56x-24=-24\)

\(-48x^2+56x=-24+24\)

\(-48x^2+56=0\)

\(\Rightarrow\orbr{\begin{cases}x=0\\x=\frac{7}{6}\end{cases}}\)

mình ko chắc

Bài 1

A, 11/24

B, -1

chúc bn học tốt

         \(x^2-5x-4\left(x-5\right)=0\)

\(\Leftrightarrow\)\(x\left(x-5\right)-4\left(x-5\right)=0\)

\(\Leftrightarrow\)\(\left(x-5\right)\left(x-4\right)=0\)

\(\Leftrightarrow\)\(\orbr{\begin{cases}x-5=0\\x-4=0\end{cases}}\)

\(\Leftrightarrow\)\(\orbr{\begin{cases}x=5\\x=4\end{cases}}\)

Vậy....

\(2x\left(x+6\right)=7x+42\)

\(\Leftrightarrow\)\(2x\left(x+6\right)-7x-42=0\)

\(\Leftrightarrow\)\(2x\left(x+6\right)-7\left(x+6\right)=0\)

\(\Leftrightarrow\)\(\left(x+6\right)\left(2x-7\right)=0\)

\(\Leftrightarrow\)\(\orbr{\begin{cases}x+6=0\\2x-7=0\end{cases}}\)

\(\Leftrightarrow\)\(\orbr{\begin{cases}x=-6\\x=\frac{7}{2}\end{cases}}\)

Vậy......

\(x^3-5x^2+x-5=0\)

\(\Leftrightarrow\)\(x^2\left(x-5\right)+\left(x-5\right)=0\)

\(\Leftrightarrow\)\(\left(x-5\right)\left(x^2+1\right)=0\)

\(\Leftrightarrow\)\(x-5=0\)

\(\Leftrightarrow\)\(x=5\)

\(x^4-2x^3+10x^2-20x=0\)

\(\Leftrightarrow\)\(x^3\left(x-2\right)+10x\left(x-2\right)=0\)

\(\Leftrightarrow\)\(x\left(x-2\right)\left(x^2+10\right)=0\)

\(\Leftrightarrow\)\(\orbr{\begin{cases}x=0\\x-2=0\end{cases}}\)

\(\Leftrightarrow\)\(\orbr{\begin{cases}x=0\\x=2\end{cases}}\)

Vậy...

b: 4x^2-20x+25=(x-3)^2

=>(2x-5)^2=(x-3)^2

=>(2x-5)^2-(x-3)^2=0

=>(2x-5-x+3)(2x-5+x-3)=0

=>(3x-8)(x-2)=0

=>x=8/3 hoặc x=2

c: x+x^2-x^3-x^4=0

=>x(x+1)-x^3(x+1)=0

=>(x+1)(x-x^3)=0

=>(x^3-x)(x+1)=0

=>x(x-1)(x+1)^2=0

=>\(x\in\left\{0;1;-1\right\}\)

d: 2x^3+3x^2+2x+3=0

=>x^2(2x+3)+(2x+3)=0

=>(2x+3)(x^2+1)=0

=>2x+3=0

=>x=-3/2

a: =>x^2(5x-7)-3(5x-7)=0

=>(5x-7)(x^2-3)=0

=>\(x\in\left\{\dfrac{7}{5};\sqrt{3};-\sqrt{3}\right\}\)

a. x(x-5) -4x+20=0

<=> x(x-5) - 4(x-5)=0

<=> (x-5)(x-4)=0

<=>(x-5)=0 hoặc x-4=0

<=> x=5 hoặc x=4

Vậy x={4;5}

b.tương tự

c. x³-5x²+x-5 =0

<=> x²(x-5) + (x-5) = 0

<=> (x-5) (x²+1) = 0

<=> x-5=0 hoặc x²+1=0(loại vì x²=-1)

<=> x=5

vậy x=5

d. bạn kiểm tra lại đề

Tìm x :

a) \(x\left(x-5\right)-4x+20=0\)

\(\Leftrightarrow x^2-5x-4x+20=0\)

\(\Leftrightarrow\left(x^2-5x\right)-\left(4x-20\right)=0\)

\(\Leftrightarrow x\left(x-5\right)-4\left(x-5\right)=0\)

\(\Leftrightarrow\left(x-4\right)\left(x-5\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-4=0\\x-5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=4\\x=5\end{matrix}\right.\)

b) \(x\left(x+6\right)-7x-42=0\)

\(\Leftrightarrow x^2+6x-7x-42=0\)

\(\Leftrightarrow\left(x^2+6x\right)-\left(7x+42\right)=0\)

\(\Leftrightarrow x\left(x+6\right)-7\left(x+6\right)=0\)

\(\Leftrightarrow\left(x-7\right)\left(x+6\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-7=0\\x+6=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=7\\x=-6\end{matrix}\right.\)

c) \(x^3-5x^2+x-5=0\)

\(\Leftrightarrow\left(x^3-5x^2\right)+\left(x-5\right)=0\)

\(\Leftrightarrow x^2\left(x-5\right)+\left(x-5\right)=0\)

\(\Leftrightarrow\left(x^2+1\right)\left(x-5\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x^2+1=0\\x-5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x^2=-1\left(vôlí\right)\\x=5\end{matrix}\right.\)

d) \(x^4-2x^3+10x^2-20x=0\)

\(\Leftrightarrow\left(x^4-2x^3\right)+\left(10x^2-20x\right)=0\)

\(\Leftrightarrow x^3\left(x-2\right)+10x\left(x-2\right)=0\)

\(\Leftrightarrow\left(x^3+10x\right)\left(x-2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-2=0\\x^3+10x=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x\left(x^2+10\right)=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=0\\x^2+10=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=0\\x^2=-10\left(vôlí\right)|x^2\ge0\forall x\end{matrix}\right.\)

a: =>-2x=-8

hay x=4

b: =>7x=-21

hay x=-3

c: =>0,25x=-1,5

hay x=-6

d: =>5,3x=6,36

hay x=6/5

e: =>-4x=-12

hay x=3

f: =>-10x=-10

hay x=1

g: =>2x+2-3-2x=0

=>-1=0(vô lý)

h: =>3-3x+4x-3=0

=>x=0

a,

\(3-x=x-5\\ \Leftrightarrow3x-x+5=0\Leftrightarrow2x+5=0\)

\(\Rightarrow x=-\dfrac{5}{2}\)

b, \(\Rightarrow x=-\dfrac{21}{7}=-3\)

c, \(\Leftrightarrow x=\left(0-1,5\right):0,25=-6\)

a. <=> 2x=8 hay x=4

b.<=> x= -21/7 = -3

c. <=> x= -1,5/ 0,25=-6

d. <=> x= -6,36/-5,3=1,2

e.<=> 4x=12 hay x= 3

f. <=> 10x = 10 hay x = 1

g. <=> 2x +2 = 3 + 2x

<=> 2=3 ( vô lí )

h.<=> 3 - 3x + 4x -3 =0

<=> x=0