Let's make the equation equal something other than 0. Let's subtract 18x from both sides.
X²=-18x
By looking at this, I can findn what x is. Since one side is a number times itself equals -18 times something else. X has to be negative 18. Let's try it.
(-18)²=-18×-18
324=324
Now let's put it into the equation.
(-18)²+18(-18)=0
324-324=0
0=0
This is the same thing, since being squared is the number multiplied by itself.
So, x equals -18.
