MathDB
2006 China Second Round Olympiad Test 1 #1

Source:

September 28, 2014

Problem Statement

Let ABC\triangle ABC be a given triangle. If BAtBCAC|BA-tBC| \ge |AC| for any tRt \in \mathbb{R}, then ABC\triangle ABC is <spanclass=latexbold>(A)</span> an acute triangle<spanclass=latexbold>(B)</span> an obtuse triangle<spanclass=latexbold>(C)</span> a right triangle<spanclass=latexbold>(D)</span> not known <span class='latex-bold'>(A)</span>\ \text{an acute triangle}\qquad<span class='latex-bold'>(B)</span>\ \text{an obtuse triangle}\qquad<span class='latex-bold'>(C)</span>\ \text{a right triangle}\qquad<span class='latex-bold'>(D)</span>\ \text{not known}\qquad