## cúiiiiiii 20 lun nè nhanh thì lụm nha 3x^2+5x-7=0

Question

cúiiiiiii
20 lun nè
nhanh thì lụm nha
3x^2+5x-7=0

in progress 0
2 tháng 2021-10-21T06:30:28+00:00 2 Answers 5 views 0

## Answers ( )

1. Đáp án:

$$\left[ \begin{array}{l}x=\frac{-5 – √109}{6} \\x=\frac{-5 + √109}{6} \end{array} \right.$$

Giải thích các bước giải:

3x² + 5x – 7 = 0

⇔ $$\left[ \begin{array}{l}x=\frac{-5 – √109}{6} \\x=\frac{-5 + √109}{6} \end{array} \right.$$

2. $3x² +5x -7 = 0$

$⇔ (\sqrt{3}x + \dfrac{5\sqrt{3}}{6})² – \dfrac{109}{12} = 0$

$⇔ (\sqrt{3}x + \dfrac{5\sqrt{3}}{6} – \sqrt{\dfrac{109}{12}}).(\sqrt{3}x + \dfrac{5\sqrt{3}}{6} + \sqrt{\dfrac{109}{12}}) = 0$

$⇔ \left[ \begin{array}{l}\sqrt{3}x + \dfrac{5\sqrt{3}}{6} – \sqrt{\dfrac{109}{12}}=0\\\sqrt{3}x + \dfrac{5\sqrt{3}}{6} + \sqrt{\dfrac{109}{12}}=0\end{array} \right. ⇔ \left[ \begin{array}{l}x=\dfrac{-5 + \sqrt{109}}{6}\\x=\dfrac{-5 – \sqrt{109}}{6}\end{array} \right.$

$\text {Vậy S = {$\dfrac{-5 – \sqrt{109}}{6}$;$\dfrac{-5 + \sqrt{109}}{6}$}}$