20000000+20000000x+x(20000000+20000000x)=24200000

Bài làm:

 20000000 + 20000000x + x(2000000 + 20000000x) = 24200000

⇔ 20000000 + 20000000x + 20000000x + 20000000x² = 24200000

⇔ 20000000x² + 40000000x – 4200000 = 0

⇔ 100x² + 200x – 21 = 0

⇔ 100x² – 10x + 210x – 21 = 0

⇔ 10x( 10x – 1 ) + 21( 10x – 1) = 0

⇔ (10x + 21)(10x – 1) = 0

⇔ \(\left[ \begin{array}{l}10x+21=0\\10x-1=0\end{array} \right.\) 

⇔ \(\left[ \begin{array}{l}10x=-21\\10x=1\end{array} \right.\) 

⇔ \(\left[ \begin{array}{l}x=\frac{-21}{10}\\x=\frac{1}{10}\end{array} \right.\) 

Vậy tập nghiệm của phương trình là: S = { $\frac{-21}{10}$ ; $\frac{1}{10}$ }