Part (a)
Plug in y = 0 and solve for x. Use the zero product property
y = x(x+3)(x-2)
0 = x(x+3)(x-2)
x(x+3)(x-2) = 0
x = 0 or x+3 = 0 or x-2 = 0 .... zero product property
x = 0 or x = -3 or x = 2
The three roots or zeros are x = 0 or x = -3 or x = 2
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Part (b)
The roots of the graph are: x = -2, x = 1, x = 3. Each root is where the graph crosses or touches the horizontal x axis.
Note how x = 0 is found in part (a), but not found here. This is one example where the graphs don't match. Another would be x = -3 is in part (a), but not here.
So that's why the graph does not match with the function in part (a)