Tag Archives: plane geometry

Moon Quarters Problem

This is a straight-forward problem from the Scottish Mathematical Council (SMC) Senior Mathematics Challenge.

“A circle has radius 1 cm and AB is a diameter.  Two circular arcs of equal radius are drawn with centres A and B.  These arcs meet on the circle as shown.  Calculate the shaded area.”

There are several possible approaches and the SMC offers two examples.

See the Moon Quarters Problem

Max Angle Puzzle

Here is a familiar puzzle from the Mathigon Puzzle Calendars for 2021.

“Given a line and two points A and B, which point P on the line forms the largest angle APB?”

See the Max Angle Puzzle

An excellent application of the solution to this puzzle can be found at Numberphile, where Ben Sparks explains an optimal rugby goal-kicking strategy.

(Update 3/23/2023)  Solution Construction

Continue reading

Covering Rectangle Puzzle

This is a nice puzzle from the Maths Masters team, Burkard Polster (aka Mathologer) and Marty Ross as part of their “Summer Quizzes” offerings.

“In the picture does the green rectangle cover more or less than half of the [congruent] red rectangle?”

It is evident from the problem solution that the two rectangles are the same, so I made it explicit.

See the Covering Rectangle Puzzle

Linked Triangles Problem

I found this problem from the 1981 Canadian Math Society’s magazine, Crux Mathematicorum, to be quite challenging.

Proposed by Kaidy Tan, Fukien Teachers’ University, Foochow, Fukien, China.

An isosceles triangle has vertex A and base BC. Through a point F on AB, a perpendicular to AB is drawn to meet AC in E and BC produced in D. Prove synthetically that

Area of AFE = 2 Area of CDE   if and only if  AF = CD.”

See the Linked Triangles Problem

(Update 2/22/2023, 6/9/2023) Alternative Solutions

Continue reading

Three Triangles Puzzle

This is a nice little puzzle from the late Nick Berry’s Datagenetics Blog.

“A quick little puzzle this week. (I tried to track down the original source, but reached a dead-end with a web search as the site that hosted it, a blogspot page under the name fivetriangles appears password protected, and no longer maintained). …

There are three identical triangles with aligned bases (in the original problem, it is stated they are equilateral, but I don’t think that really matters; Any congruent triangles will do, and I’m going to use isosceles triangles in my solving). If we say that one triangle has the area A, what is the area of the two shaded regions?”

See the Three Triangles Puzzle.

Wisdom of Old

Here is another Brainteaser from the Quantum magazine.

“King Arthur ordered a pattern for his quarter-circle shield. He wanted it to be painted in three colors: yellow, the color of kindness; red, the color of courage: and blue the color of wisdom. When the artist brought in his work, the king’s armor-bearer said there was more courage than wisdom on the shield. But the artist managed to prove that the proportions of both virtues were equal. Can you tell how? (A. Savin)”

This is another relatively simple problem, though it may look a bit daunting at first.

See Wisdom of Old