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P12 [Algebra] - Turkish NMO 1st Round - 2002

Source:

August 8, 2014

Problem Statement

What is the least possible value of ab+bc+acab + bc + ac such that a2+b2+c2=1a^2 + b^2 + c^2 = 1 where a,b,ca,b,c are real numbers?
<spanclass=latexbold>a)</span> 1<spanclass=latexbold>b)</span> 12<spanclass=latexbold>c)</span> 13<spanclass=latexbold>d)</span> 122<spanclass=latexbold>e)</span> 0 <span class='latex-bold'>a)</span>\ -1 \qquad<span class='latex-bold'>b)</span>\ -\dfrac 12 \qquad<span class='latex-bold'>c)</span>\ -\dfrac 13 \qquad<span class='latex-bold'>d)</span>\ -\dfrac{1}{2\sqrt 2} \qquad<span class='latex-bold'>e)</span>\ 0