The zeroes of the function are the values of x at f(x) = 0
So equate f(x) by 0 at first
Now we should factorize the quadratic into two factors
Since the last term is positive so the two brackets have the same signs
Since the middle term is positive then the two bracket has +
(x + ?)(x + ?) = 0
We need to find two numbers their product is 21 and their sum is 10
They are 7 and 3
7 * 3 = 21 and 7 + 3 = 10
(x + 3) (x + 7) = 0
Now equate each bracket by 0 to find the values of x
(x + 3) = 0
Subtract 3 from both sides
x + 3 - 3 = 0 -