Skip to main content

2010 AMC 10A Problem 16

Problem 16 of 25IntermediateAlgebraGeometry

Nondegenerate ABC\triangle ABC has integer side lengths, BD\overline{BD} is an angle bisector, AD=3,AD = 3, and DC=8.DC = 8. What is the smallest possible value of the perimeter?

Answer choices

Show solution

Solution

Using the Angle Bisector Theorem, we have that AB3=BC8 \dfrac{AB}{3} = \dfrac{BC}{8} AB=38BC. AB = \dfrac{3}{8} BC. For ABAB and BCBC to be integers, we must have that BCBC is a multiple of 8.8. To minimize the perimeter, we can set BC=8BC = 8 and AB=3.AB = 3. This, however, makes the triangle degenerate. BCBC must then be 1616 and AB=6.AB = 6. Since AC=AD+DC=11,AC = AD + DC = 11, the perimeter is 16+6+11=33. 16 + 6 + 11 = 33. Thus, B is the correct answer.

More practice

Concepts: angle bisector theorem · triangle inequality · optimization

Problem text and solution from the LIVE past-contest archive. See also the AoPS wiki page for community solutions.