Getting a quadratic equation from the x-intercepts

The graph of a quadratic function f(x) intersects the x-axis at -3 and 5.  
What is a possible equation for f(x)?

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Work backwards from the x-intercepts to arrive at the equation.

x = -3   and   x = 5
x + 3 = 0   and   x - 5 = 0   {added 3 to each side of first equation and added 5 to each side of second equation}
(x + 3)(x - 5) = 0   {multiplied the two binomials together and set equal to zero}
x² - 2x - 15 = 0   {muliplied the two binomials using FOIL method or distributive property}

f(x) = x² - 2x - 15   {replaced 0 with f(x) to write in function notation}
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