Work backwards to write a quadratic equation that will have solutions of x = 3 and x = -7.

x² + 4x - 21

Step-by-step explanation:

Given the solutions of x = 3 and x = -7, moving the constant to the other side and setting both equations equal to '0':

x - 3 = 0 and x + 7 = 0

So, the two binomials that make up the quadratic are:

(x - 3)(x + 7)

Use FOIL:  x² + 7x - 3x - 21

Combine like terms: x² + 4x - 21