Math CentralQuandaries & Queries


Question from Katelyn, a student:

Write the quadratic equation....

Sum of the roots = 16
Product of the roots = -80

Hi Katelyn,

Let's work backwards. Suppose that you have a quadratic with roots a and b then you know the quadratic is

(x - a)(x - b)

Expanding this you get

x2 - (a + b)x + ab

Said in another way the quadratic is

x2 - (the sum of the roots)x + (the product of the roots)


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