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f(x) = x^{2} - 4x - 21

Which of the following is an equivalent form of the function f above in which the zeros of f appears as constants or coefficients?

A. f(x) = (x - 2)^{2} - 25

B. f(x) = x(x - 4) - 21

C. f(x) = (x + 1)(x - 5) - 16

D. f(x) = (x + 3)(x - 7)

**Comments**

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f(x) = x^{2} - 4x - 21

The above is a quadratic equation and can be simplified by factorization

f(x) = x^{2} + 3x - 7x - 21

f(x) = (x^{2} + 3x) - (7x + 21)

f(x) = x(x + 3) - 7(x + 3)

f(x) = (x + 3)(x - 7)

**Answer: D**

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