4x^2-25-(2x-5)(2x+7)=0 
<=> 4x^2 - 25 - (4x^2 + 14x - 10x - 35) = 0 
<=> 4x^2 - 25 - 4x^2 - 14x + 10x + 35 = 0 
<=> -4x + 10 = 0 
<=> x = -10/-4 
<=> x = 5/2

  4x^2-25-(2x-5)(2x+7)=0 
<=> 4x^2 - 25 - (4x^2 + 14x - 10x - 35) = 0 
<=> 4x^2 - 25 - 4x^2 - 14x + 10x + 35 = 0 
<=> -4x + 10 = 0 
<=> x = -10/-4 
<=> x = 5/2

\(4x^2-25-\left(2x-5\right)\left(2x+7\right)=0\\ \Leftrightarrow4x^2-25-\left(4x^2+14x-10x-35\right)=0\\ \Leftrightarrow4x^2-25-4x^2-14x+10x+35=0\\ \Leftrightarrow-4x+10=0\)
\(\Leftrightarrow x=\frac{-10}{-4}\\ \Leftrightarrow x=\frac{5}{2}\)

4x² - 25 - 5(2x + 7 ) = 0

=> 4x² - 25 - 10x - 35 = 0

=> 4x² - 10x - 60 = 0 

đến dố bạn tự giải nốt nha sử dụng pt hoặc tính dấy là ra 

Study well 

mk ko bt 123

Suy ra (2x-4)-(3x-3×5)=1 Suy ra(2x-4)-3x+15=1 Suy ra 2x-4-3x+15=1 Suy ra (2x-3x)+(15-4)=1 -1x+11=1 1-11=-1x -1x=-10 X=10

mình sửa đề chút nha!   

     4x^2 - 25 - (2x - 5)(2x + 7) = 0

<=>(2x - 5)(2x + 5) - (2x - 5)(2x + 7) = 0

<=>(2x - 5)(2x + 5 - 2x -7) = 0

<=> -2(2x - 5) = 0

<=> -4x + 10 = 0

<=>  -4x        = -10

<=>         x    = 5/2  

Thiếu rồi

\(\left(5x-2\right)\left(2x+7\right)-4x^2-25=0\)

\(10x+35-4x^2-14x-4x^2+25=0\)

\(-4x+60-8x^2=0\)

\(-4\left(2x^2+x-15\right)=0\)

\(-4\left(2x^2+6x-5x-15\right)=0\)

\(-4\left(2x-5\right)\left(x+3\right)=0\)

=> \(x\) ∈ \(\left\{\dfrac{5}{2};-3\right\}\)

8x²+30x+7=0

 8x²+16x+14x+7=0

8x(x+2) +7(x+2)=0

(8x+7)(x+2)=0

=>\(\orbr{\begin{cases}8x+7=0\\x+2=0\end{cases}\Rightarrow\orbr{\begin{cases}x=-\frac{7}{8}\\x=-2\end{cases}}}\)

a)

4x²-8x+4=2(1-x)(x+1)

4x²-8x+4-2+2x²=0

6x²-8x+2=0

2(3x²-4x+1)=0

3x²-3x-x+1=0

3x(x-1) -(x-1)=0

(3x-1)(x-1)=0

\(\Rightarrow\orbr{\begin{cases}3x-1=0\\x-1=0\end{cases}\Rightarrow\orbr{\begin{cases}x=\frac{1}{3}\\x=1\end{cases}}}\)

4x² - 25 - (2x - 5)(2x + 7) = 0

<=> (2x)² - 5² - (2x - 5)(2x + 7) = 0

<=> (2x - 5)(2x + 5) - (2x - 5)(2x + 7) = 0

<=> (2x - 5)(2x + 5 - 2x - 7) = 0

<=> (2x - 5) . (-2) = 0

<=> 2x - 5 = 0

<=> 2x = 5

<=> x = 5/2

\(o,x^2-9x+20=0\)

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

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

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

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

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

\(n,3x^3-3x^2-6x=0\)

\(\Leftrightarrow3x\left(x^2-x-2\right)=0\)

\(\Leftrightarrow3x\left(x^2+x-2x-2\right)=0\)

\(\Leftrightarrow3x\left[x\left(x+1\right)-2\left(x+1\right)\right]=0\)

\(\Leftrightarrow3x\left(x+1\right)\left(x-2\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}\orbr{\begin{cases}3x=0\\x+1=0\end{cases}}\\x-2=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}\orbr{\begin{cases}x=0\\x=-1\end{cases}}\\x=2\end{cases}}\)

-_- bài này hôm qua lm rùi