When faced with this form of quadratic equation where the leading term is x², all we have to do is ask ourselves what are the factors of the constant term that when added, will result to the second term?
Let's list down the factors of our constant term -21.
These are: 1 and -21, -1 and 21, 3 and 7, -3 and 7.
Let's add each factor.
1 + -21 = -20
-1 +21 = 20
3 + 7 = 10
-3 + 7 = -4
Therefore, the factors of the above equation are:
The values of x are:
x - 3 = 0
x = 3
x + 7 = 0
x = -7