Step-by-step explanation: A common mistake in this problem would be to say that if x² = 121, x must equal 11.
However, you must set the equation equal to 0 first.
So our first step is to subtract 121 from both sides to get x² - 121 = 0.
Next, factor the left side to get (x + 11)(x - 11) = 0
So either x + 11 = 0 or x - 11 = 0.
Solving each equation from here, we find that x = -11 or x = 11.
So our answer is not just 11, it's {11, -11}.