For this case we have that by definition, the quadratic formula is:[tex]x = \frac {-b \pm \sqrt {b ^ 2-4 (a) (c)}} {2a}[/tex]
A quadratic equation is of the form:
[tex]ax ^ 2 + bx + c = 0[/tex]
Option A: This equation can be solved without the quadratic formula
[tex]x ^ 2 = \frac {9} {3}\\x ^ 2 = 3\\x = \pm \sqrt {3}[/tex]
Option B:
This equation is not as easy to solve by factoring or as option A. We can use the quadratic formula.
Option C:
[tex]-2x ^ 2 + 5x = 7[/tex]
Similarly, this equation can be solved with the quadratic formula
Option D:
[tex]- (x - 3) (x + 9) = 0[/tex]
In this factored equation we can see that the roots are
[tex]x_ {1} = 3\\x_ {2} = - 9[/tex]
Answer:
Option B, C
