Answers: p = 3 or p = -2
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Work Shown
Method 1
p^2 - p - 6 = 0
(p - 3)(p + 2) = 0
p-3 = 0 or p+2 = 0
p = 3 or p = -2
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Method 2
Replace p with x to get the equation x^2 - x - 6 = 0
Compare that to the template ax^2 + bx + c = 0
a = 1, b = -1, c = -6 are plugged into the quadratic formula.

Therefore p = 3 or p = -2 are the two answers.
The quadratic formula takes a bit longer, but it is guaranteed to always work. Whereas factoring is a trial-and-error approach which may not always work. Even if it does work, factoring still requires guessing.