A Tangent and an Intersection

Problem

Let f(x)=(x+t)ln⁡xf(x) = (x + t)\ln x, and suppose the tangent line to f(x)f(x) at x=1x = 1 is parallel to the line x−y=0x - y = 0.

1. Find tt, and find the intervals on which f(x)f(x) is monotonic. 2. Let a>0a > 0. If the graphs of y=eaxy = \mathrm{e}^{ax} and y=f(1x)axy = \dfrac{f\left(\frac{1}{x}\right)}{ax} intersect for some x∈(0,1e)x \in \left(0, \dfrac{1}{\mathrm{e}}\right), find the range of possible values of aa.

Answer

Solution

Difficulty7/10
Topicsfunctions, Extrema, calculus, Tangent Line Trick, Monotonicity

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