contestada

Select all of the following that are quadratic equations.
3x ^2 + 5x - 7 = 0
x ^3 - 2x ^2 + 1 = 0
2x - 1 = 0
5x ^2+ 15x = 0
6x - 1 = 4x + 7
x ^2 - 4x = 4x + 7