Hi, I have a question for the above topic.

Let p(x) =5x^3 -23x^2 + x + 6 be a polynomial. Then all zeros of p(x) lies in [-M,M]. Find the value of M to 2 d.p.

My solution

p(x) = x^3 - (23/5)x^2 + (1/5)x +6/5

M = 1 + max{|-23/5|, |1/5|,|6/5|}

= 1 + 23/5 =5.6

Here, i am not sure if i should divide the constant 6 by the leading coefficient which is 5. If i don't divide, then M = 1 + 6 = 7.

So, which is the correct one?