Maths Olympiad Prep

Track / Stage 3 / 71 of 260 #71 of 1964

Problem 71

AMC 10/12, early questions
Geometry Difficulty 3.2 Multiple choice

Lines in the xyxy-plane are drawn through the point (3,4)(3,4) and the trisection points of the line segment joining the points (4,5)(-4,5) and (5,1)(5,-1). One of these lines has the equation

Pick one

Official solution

The trisection points of (4,5)(-4, 5) and (5,1)(5, -1) can be found by trisecting the x-coordinates and the y-coordinates separately. The difference of the x-coordinates is 99, so the trisection points happen at 4+93-4 + \frac{9}{3} and 4+93+93-4 + \frac{9}{3} + \frac{9}{3}, which are 1-1 and 22. Similarly, the y-coordinates have a difference of 66, so the trisections happen at 33 and 11. So, the two points are (1,3)(-1, 3) and (2,1)(2, 1).
We now check which line has both (3,4)(3, 4) and one of the two trisection points on it. Plugging in (x,y)=(3,4)(x, y) = (3, 4) into all five of the equations works. The point (2,1)(2, 1) doesn't work in any of the five lines. However, (1,3)(-1, 3) works in line EE. Thus, the answer is E\fbox{E}

Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic, difficulty and ordering added by this site.