Question

Which two equations would be most appropriately solved by using the quadratic formula?

Answer 1

For this case we have that by definition, the quadratic formula is:$x = \frac {-b \pm \sqrt {b ^ 2-4 (a) (c)}} {2a}$

A quadratic equation is of the form:

$ax ^ 2 + bx + c = 0$

Option A: This equation can be solved without the quadratic formula

$x ^ 2 = \frac {9} {3}\\x ^ 2 = 3\\x = \pm \sqrt {3}$

Option B:

This equation is not as easy to solve by factoring or as option A. We can use the quadratic formula.

Option C:

$-2x ^ 2 + 5x = 7$

Similarly, this equation can be solved with the quadratic formula

Option D:

$- (x - 3) (x + 9) = 0$

In this factored equation we can see that the roots are

$x_ {1} = 3\\x_ {2} = - 9$

Answer:

Option B, C