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

\(=4x^2-25-\left(4x^2+4x-35\right)\)

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

\(=35-25-4x\)

\(=10-4x\)

\(=2\left(5-2x\right)\)

  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

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

Ta có đa thức tương đương: 4x²-25+10x-4x²+35-14x

=-4x+10=-2(2x+5)

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

\(\Leftrightarrow-\left(2x-5\right).\left(2x+7\right)-\left(2x+5\right)\left(2x-5\right)=0\)

\(\Leftrightarrow\left(2x-5\right)\left(-7-2x-2x-5\right)=0\)

\(\Leftrightarrow\left(2x-5\right)\left(-12-4x\right)=0\)\(\Leftrightarrow\orbr{\begin{cases}2x-5=0\\-12-4x=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=\frac{5}{2}\\x=-3\end{cases}}\)

Vậy x=5/2 hoặc x=-3

Thiếu rồi

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

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

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

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

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

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

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

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

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

\(=-4x+10=2\left(-2x+5\right)\)

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

\(\Rightarrow\left(2x\right)^2-5^2=\left(2x-5\right).\left(2x+7\right)\)

\(\Rightarrow\left(2x-5\right).\left(2x+5\right)-\left(2x-5\right).\left(2x+7\right)=0\)

\(\Rightarrow\left(2x-5\right).\left(2x+5-2x-7\right)=0\)

\(\Rightarrow\left(2x-5\right).\left(-2\right)=0\)

Vì \(-2\ne0.\)

\(\Rightarrow2x-5=0\)

\(\Rightarrow2x=0+5\)

\(\Rightarrow2x=5\)

\(\Rightarrow x=5:2\)

\(\Rightarrow x=\frac{5}{2}\)

Vậy \(x=\frac{5}{2}.\)

Chúc bạn học tốt!

4x²−25 - ( 4x² + 14x -10x - 35) = 0

4x² −25 - 4x² -14x + 10x + 35 = 0

-4x + 10 = 0

=> x = -\(\frac{5}{2}\)

Vậy x = -\(\frac{5}{2}\)

Câu này bình thường mà bạn có thẻ giải bằng cách dùng hàng đẳng thức số 3 hoặc nhân tung vào như vậy cũng đc

\(=\left(2x-5\right)\left(2x+5\right)-\left(2x-5\right)\left(2x+7\right)\)

\(=\left(2x-5\right)\left(2x+5-2x-7\right)\)

\(=-2\left(2x-5\right)\)