Question

Solve the equation by factoring: x2 − 7x + 12 = 0

Answer 1

Answer:

x = 3 . . . or . . . x = 4

Step-by-step explanation:

The factored form is ...

(x -3)(x -4) = 0

The zero product rule tells you the solutions are the values of x that make the factors be zero:

x = 3

x = 4

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Comment on factoring

When the leading coefficient is 1, the coefficient of the x-term is the sum of the constants in the binomial factors, and the constant term is their product. You can see this by multiplying out the generic case:

(x +a)(x +b) = x^2 +(a+b)x + ab

What this means is that when you're factoring, you're looking for factors of the constant that add up to give the coefficient of the x-term. Here, the x-term is negative and the constant is positive, so both factors will be negative.

12 = -1×-12 = -2×-6 = -3×-4

The sums of these factor pairs are -13, -8, -7. Clearly, the last pair of factors of 12 will be useful to us, since that sum is -7. So, the binomial factors of our equation are ...

(x -3)(x -4) = 0

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If the leading coefficient is not zero, the method of factoring is similar, but slightly different. Numerous videos and web sites discuss the method(s).