The factored form of the equation is f(x) = (x - 2)(x + 10), which makes the zeros of the function x = -10 and x = 2.
In order to factor a quadratic like this, you must find factors of the constant (in this case -20). The pairs of factors are listed below.
1 and -20
-1 and 20
2 and -10
-2 and 10
4 and -5
-4 and 5
Now we must pick out the pair that add to the coefficient of x.
1 and -20
-1 and 20
2 and -10
-2 and 10
4 and -5
-4 and 5
Once you've picked out those numbers, you can place each in a parenthesis with x.
f(x) = (x - 2)(x + 10)
Then to find the zeros to the equation, set each parenthesis equal to 0 and solve.
x - 2 = 0
x = 2
x + 10 = 0
x = -10
