Solve quadratic equation
Given quadratic equation:
`ax^2+bx+c = 0`
where `a, b` and `c` are constant.
`x = (-b±sqrt(b^2-4ac))/(2a)`
Example 1:
`x^2+4x - 5 = 0`
`x = (-4±sqrt(4^2-4times(-5)))/2`
`x=(-4±sqrt(36))/2`
`x= (-4 ± 6)/2`
`x=1` or `x = -5`
Example 2:
`-2x^2 -3x +9 = 4`
`=>-2x^2 -3x +9 - 4=0`
`=>-2x^2 -3x +5 = 0`
`x=(3±sqrt((-3)^2-4(-2)(5)))/(2times(-2))`
`x=(3±7)/(-4)`
`x=-2.5` or `x=1`