(2x + 5)2 - (4x - 3) = 20
<=> 4x2 + 20x + 25 - 4x + 3 = 20
<=> 4x2 + 16x + 28 - 20 = 0
<=> 4x2 + 16x + 8 = 0
<=> 4x2 + 16x + 16 - 8 = 0
<=> (2x + 4)2 - 8 = 0
<=> (2x + 4 -\(\sqrt{8}\))(2x + 4 +\(\sqrt{8}\)) = 0
<=> 2x + 4 -\(\sqrt{8}\)= 0 hay 2x + 4 +\(\sqrt{8}\)= 0
<=> 2x = \(\sqrt{8}\)- 4 I 2x = -\(\sqrt{8}\)-4
<=> x = \(\frac{\sqrt{8}-4}{2}\) I x = \(\frac{-\sqrt{8}-4}{2}\)
\(\left(2x+5\right)^2-\left(4x-3\right)=20\)
\(4x^2+20x+25-4x+3=20\)
\(4x^2+16x+28=20\)
\(\left(2x\right)^2+16x+16-8=0\)
\(\left(2x+4\right)^2=8=\sqrt{8}^2\)
\(\Rightarrow2x+4=\sqrt{8}\)
\(\Rightarrow x=\frac{\sqrt{8}-4}{2}\)
