Question

Which of the following equations has only one solution?

x^2 + 4x + 4 = 0

x^2 + x = 0

x^2 - 1 = 0

Answer 1

If you're allowed to use graphing calculators, the simplest method is to graph each of the equations and see which touch the x-axis at one point only.

However, as that probably won't be allowed on tests, you can also factor the equations.

1. (x+2)(x+2) = 0
x = -2

2. x(x+1) = 0
So, x = 0 and x = -1

3. x^2 = 1
So, x = -1 and x = 1