Math CentralQuandaries & Queries


Question from Ashley, a student:

I have to solve using the quadratic formula. And my answer should be in simplest exact form. And I can't approximate.
I really need help to prepare for a test ....
x(x-3) = 5 (x+4)

Hi Ashley,

To use the quadratic formula you need the the quadratic equation in the form $a x^2 + b x + c = 0.$ To obtain this from your equation first expand both sides to get

\[x(x-3) = 5 (x+4) = x^2 - 3x = 5x + 20\]

and then subtract $5x + 20$ from both sides and simplify. Now you should be able to use the quadratic formula.


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