A Shared Point Forces a Minimum

Problem

Let a,bRa,b\in\mathbb R with a0a\neq 0. The curves

y=a+2xandy=ax+2b+1y=\frac{a+2}{x}\qquad\text{and}\qquad y=ax+2b+1

have at least one common point with xx-coordinate in the interval [3,4][3,4]. Find the minimum value of a2+b2a^2+b^2.

Answer

Solution

Difficulty8/10
TopicsExtrema, Substitution, Monotonicity, algebra, inequality

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