Answer: zeros are -4 and -5
Explanation:
(x^2 + 9x + 20) we can split 9x into 4x + 5x
x^2 + 4x + 5x + 20 now we can factor out some values
first for x^2 + 4x we can take out an x which makes it x(x+4)
now for 5x + 20 we can factor out 5 which makes it 5(x+4)
the function is now x( x + 4 ) + 5(x + 4), and we can factor out (x + 4)
so (x+4)(x+5) if x = -4 f(x) = 0 and if x = -5 f(x) = 0