Khủng giúp mình giải PT cực khó!

D

dung495

[tex]x^2 - 5x - 9=0[/tex]
<=>[tex]x^2 - 2.\frac{5x}{2} +(\frac{5}{2})^2 - \frac{25}{4} - 9=0[/tex]
<=>[tex](x-\frac{5}{2})^2-\frac{61}{4}=0[/tex]
<=>[tex](x-\frac{5}{2}-\frac{sqrt{61}}{2})(x-\frac{5}{2}+\frac{sqrt{61}}{2})=0[/tex]
<=>[tex]x=\frac{5+sqrt{61}}{2} hay x=\frac{5-sqrt{61}}{2}[/tex]
Nhớ thanks nha bạn
 
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