2014 AMC 10A Problem 18

Below is the professionally curated solution for Problem 18 of the 2014 AMC 10A, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2014 AMC 10A solutions, or check the answer key.

All of the real AMC 8, AMC 10, AMC 12, and AIME problems in our complete solution collection are used with official legal permission of the Mathematical Association of America (MAA).

Concepts:coordinate geometrysquare (geometry)vector

Difficulty rating: 1720

18.

A square in the coordinate plane has vertices whose yy-coordinates are 0,0, 1,1, 4,4, and 5.5. What is the area of the square?

1616

1717

2525

2626

2727

Solution:

Let one vertex be A=(0,0)A=(0,0), and let the adjacent vertex with y-coordinate 11 be B=(x,1)B=(x,1) with x>0x>0.

Rotating the side vector (x,1)(x,1) by 9090^\circ gives the next side vector (1,x)(-1,x), so another vertex has y-coordinate xx. The remaining y-coordinates are 44 and 55, hence x=4x=4.

The side length squared is AB2=x2+12=42+1=17AB^2=x^2+1^2=4^2+1=17, which is the area of the square.

Thus, B is the correct answer.

Problem 18 in Other Years