We can check our answer by substituting the given zeros for x. If the result is y=0, it means that the given numbers are actually zeros of the function and our answer is correct. Let's start by checking - 2.
y=x^3-3x^2-6x+8
y=( - 2)^3-3( - 2)^2-6( - 2)+8
y=- 8-3(4)-6(-2)+8
y=- 8-12+12+8
y=0 ✓
We proved that - 2 is a zero of the function. Let's now check 1.
y=x^3-3x^2-6x+8
y= 1^3-3( 1)^2-6( 1)+8
y=0 ✓
We have shown that 1 is also a zero. Finally, let's see what happens with 4.
y=x^3-3x^2-6x+8
y= 4^3-3( 4)^2-6( 4)+8
y=64-3(16)-6(4)+8
y=64-48-24+8
y=0 ✓
We found that 4 is also a zero. Since - 2, 1, and 4 are zeros of the polynomial function, our answer is correct.