Answer:
x = the unknown number. Its square is x2. The sum of a number and its square is 12:
x + x²= 12
Putting the quadratic into standard form:
x2 + x - 12 = 0
(x+4)(x-3) = 0
x = -4 and 3
Let's check x=-4:
x + x2 = 12
(-4) + (-4)2 = 12
-4 + 16 = 12
12 = 12
Now let's check x= 3:
x + x2 = 12
3 + 32 = 12
3 + 9 = 12
12 = 12
Yup, they both work. There are two answers, x = -4 and x = 3