solve for the roots of quadratic equation

You don't need to use the quadratic equation for that one, you use the quadratic equation when you have something in the form ax^2+bx+c=0. Solving that equation is just like any old equation from pre-algebra.

Original Equation

8x^2=72

Divide both sides by 8

x^2=9

Square root of both sides

x= + or - 3

Early I said you don't have to use the quadratic equation to solve, however you can use it if you want to.

Simply rewrite the equation so it's equal to 0.

8x^2-72=0

What you have in effect is

8x^2+0x-72=0

Your a will equal 8, b will equal 0 and c will equal -72. From there you simply plug into the formula.
 
you would only need quadratic equations if there was an extra variable in there

example:

8x^2+x=72

8b^2+db-72=0
 
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