How do I prove that f(x) = ln(x) − (x − 4)^2 has exactly two roots. I assume we take the derivative of the function. I get: y′=1/x−2(x−4) and I attempt to set it to 0 and solve but get stuck. Any tips?

charmbraqdy

charmbraqdy

Answered question

2022-11-18

How do I prove that f ( x ) = l n ( x ) ( x 4 ) 2 has exactly two roots.
I assume we take the derivative of the function. I get: y = 1 / x 2 ( x 4 ) and I attempt to set it to 0 and solve but get stuck. Any tips?

Answer & Explanation

AtticaPlotowvi

AtticaPlotowvi

Beginner2022-11-19Added 18 answers

Outline: 1) f ( 1 ) < 0, f ( 4 ) > 0, f ( 10 ) < 0, so by the Intermediate Value Theorem f ( x ) = 0 has at least two roots. 2) By the Mean Value Theorem, between any two roots of f ( x ) = 0 there is at least one root of f ( x ) = 0. 3) The equation f ( x ) = 0 has exactly one positive root.

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