Solve the equations
1) $$x^2+2x-1=0$$
2) $$4x^2-16=0$$
3) $$3x^2+6x=0$$
See development and solution
Development:
1) $$a=1$$, $$b=2$$, $$c=-1$$
$$$\displaystyle x=\frac{-2 \pm \sqrt{1+4}}{2}= \frac{-2 \pm \sqrt{5}}{2}=\left \{\begin{matrix} x_1=-2,4142 \\ x_2=0,4142\end{matrix}\right.$$$
2) $$a=4$$, $$b=0$$, $$c=-16$$
$$$\displaystyle x=\frac{-0 \pm \sqrt{0+16\cdot16}}{2\cdot4}= \frac{\pm16}{8}=\left \{\begin{matrix} x_1=2 \\ x_2=-2\end{matrix}\right.$$$
3) $$a=3$$, $$b=6$$, $$c=0$$
$$$\displaystyle x=\frac{-6 \pm \sqrt{36-0}}{2\cdot3}= \frac{-6\pm6}{6}=\left \{\begin{matrix} x_1=0 \\ x_2=-2\end{matrix}\right.$$$
Solution:
1) $$x_1=-2,4142$$, $$x_2=0,4142$$
2) $$x_1=2$$, $$x_2=-2$$
3) $$x_1=0$$, $$x_2=-2$$