Slicing a Square

Geometry Level 3

Consider a square with side length 1, whose interior is divided into three parts of equal area by two line segments.

If the sum of the slopes of these two line segments can be expressed as A B \dfrac AB , where A A and B B are coprime positive integers, determine A + B A+B .


Inspiration .


The answer is 19.

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1 solution

Geoff Pilling
Dec 8, 2016

The area of the square is 1 1 . Each of the colored regions, then, must have an area of 1 3 \frac{1}{3} . The area of each triangle is given by,

A = b a s e h e i g h t 2 = 1 3 A = \frac{base \cdot height}{2} = \frac{1}{3}

So, the height of the bottom one and the width of the top one must be 2 3 \frac{2}{3} .

So, the slope of the lower line, m 1 m1 , is 2 3 \frac{2}{3} and the slope of the upper one, m 2 m2 , is 3 2 \frac{3}{2} .

So, m 1 + m 2 = 2 3 + 3 2 = 13 6 m_1 + m_2 = \frac{2}{3} + \frac{3}{2} = \frac{13}{6}

13 + 6 = 19 13+6 = \boxed{19}

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