The Perimeter isn't as Easy as You Think!

Geometry Level 3

There is a triangle A B C \bigtriangleup ABC with sides a a , b b and c c , where a a , b b and c c satisfy the equations b + c = 8 b + c = 8 and b c = a 2 12 a + 52 bc = a^2 -12a + 52 . Find the perimeter of A B C \bigtriangleup ABC .

12 10 14 16

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1 solution

Hua Zhi Vee
Jun 9, 2017

Using Completing the Square to the equation b c = a 2 12 a + 52 bc = a^2 -12a + 52 , turn the equation into

b c = ( a 6 ) 2 + 16 bc = (a-6)^2 + 16

From the equation, we can know that b c 16 bc \geqslant 16 .

Similarly, from the equation b + c = 8 b + c = 8 , we can know that b c 16 bc \leqslant 16 .

From the two equations

b c 16 bc \geqslant 16

b c 16 bc \leqslant 16

We can know that b c = 16 bc=16

b c = ( a 6 ) 2 + 16 bc = (a-6)^2 + 16

( a 6 ) 2 = 0 (a-6)^2 = 0

a = 6 a=6

a + b + c = 14 \therefore a + b + c = 14

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