y2 + 7y + 2 = 0
\(\Leftrightarrow\) y(y + 7) + 2 = 0
\(\Leftrightarrow\) y = \(-\frac{7-\sqrt{41}}{2}\); y = \(-\frac{7+\sqrt{41}}{2}\)
*(Nâng cao): - 0.29843788... ; - 6.70156211...
Vậy y = \(-\frac{7-\sqrt{41}}{2}\); y = \(-\frac{7+\sqrt{41}}{2}\).
Chúc bạn học tốt!
\(\Leftrightarrow\left(y^2+7y+\frac{49}{4}\right)-\frac{41}{4}=0\)
\(\Leftrightarrow\left(y+\frac{7}{2}\right)^2-\sqrt{\frac{41}{4}}^2=0\)
\(\Leftrightarrow\left(y+\frac{7-\sqrt{41}}{2}\right)\left(y+\frac{7+\sqrt{41}}{2}\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}y=\frac{\sqrt{41}-7}{2}\\y=-\frac{7+\sqrt{41}}{2}\end{matrix}\right.\)