Question

A square of area $2$ is inscribed in a square of area $3,$ creating four congruent triangles, as shown below. What is the ratio of the shorter leg to the longer leg in the shaded right triangle?

$\dfrac{1}{5}$

$\dfrac{1}{4}$

$2 - \sqrt{3}$

$\sqrt{3} - \sqrt{2}$

$\sqrt{2} - 1$

Answer: C

Concepts:square (geometry)Pythagorean Theorem Vieta’s Formulas

Difficulty rating: 1500

Solution:

Each corner right triangle has legs $a$ and $b.$ A side of the outer square gives $a+b=\sqrt3,$ and a side of the inscribed square gives $a^2+b^2=2.$ Subtract to find the product: $2ab=(a+b)^2-(a^2+b^2)$ $=3-2$ $=1,$ so $ab=\tfrac12.$ Then $a$ and $b$ are the roots of $t^2-\sqrt3\,t+\tfrac12=0,$ namely $\tfrac{\sqrt3\pm1}{2}.$ The ratio of the smaller leg to the larger is $\dfrac{\sqrt3-1}{\sqrt3+1}$ $=\dfrac{(\sqrt3-1)^2}{2}$ $=2-\sqrt3.$ Thus, C is the correct answer.

2023 AMC 10A Problem 11

Answer: C

Difficulty rating: 1500

Solution:

Problem 11 in Other Years