This problem comes from the British Maths Olympiad Round 1 in 2010.
Let a, b and c be the lengths of the sides of a triangle. Suppose that ab + bc + ca = 1.
Show that (a + 1)(b + 1)(c + 1) is less than 4.
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Watch video Problem 6 from the British Maths Olympiad | Inequalities | Math Olympiad Training online without registration, duration hours minute second in high quality. This video was added by user GG Maths 14 March 2021, don't forget to share it with your friends and acquaintances, it has been viewed on our site 6,336 once and liked it 255 people.