How to solve unknown using calculus?

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Can someone please explain to me how to do question 5? Thanks!

1 Answer
Sep 25, 2017

Please see below.

Explanation:

The function f(x) = x^3-9x^2+15x

Has a local maximum of 7 at x=1 and a local minimum of -25 at x=5.

The graph is:

graph{x^3-9x^2+15x [-18.43, 32.9, -12.87, 12.8]}

In order to eliminate two of the zeros, we can either translate up by more that 25, so use w > 25

or we can translate down by more than 7, using x < -7