When the square of a certain number is decreased by 6 times the number, the result is -9. What is the number?

1 Answer

The number is 3.

Explanation:

1.Set up an equation

x^2-6x=-9

2.Set the equation equal to 0

x^2-6x=-9
x^2-6x+9=0 larrThis is a quadratic equation!

3. Solve for the unknown

Personally, I prefer the quadratic formula over factorising, so...
Plug in and simplify!

x=(-b+-sqrt(b^2-4ac))/(2a)

x=(6+-sqrt(-6^2– 4xx1xx9))/(2xx1)

x=(6+-sqrt(36 – 36))/(2)

x=(6+-sqrt(0))/(2)

x=6/2

x=3