Find the quadratic function with the given x-intercepts

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

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Work backwards from the solutions to the equation.

x = -3   and   x = 5
x + 3 = 0   and   x - 5 = 0   {added 3 and subtracted 5 in the two equations}
(x + 3)(x - 5) = 0   {multiplied the two binomials and set equal to zero}
x² - 2x - 15 = 0   {used distributive property / FOIL method}
f(x) = x² - 2x - 15   {replaced 0 with f(x)}
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