All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Shapes > Geometry
Angles missing (Posted on 2012-07-09) Difficulty: 2 of 5
What are the angles of the right-angled triangle, whose area is 1/(2*pi) of said triangle's circumscribing circle's area?

See The Solution Submitted by Ady TZIDON    
Rating: 4.0000 (1 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution solution Comment 1 of 1

As the ratio is between two areas, scale doesn't matter so let's make the radius of the circle equal 1.

The circle's area is then pi, and we want the triangle to have area 1/2. It's hypotenuse is the diameter of the circle, which is 2.

Call the legs of the triangle x and y.


xy=1 so that the area is 1/2

x^2 + y^2 = 2^2 as it's a right triangle


x^2 + 1/x^2 = 4
x^2 - 4 + 1/x^2 = 0
x^4 - 4x^2 + 1 = 0
x^2 = (4 +/- sqrt(16-4)) / 2
    = 2 +/- sqrt(3)
x = sqrt(2 +/- sqrt(3))

One of the evaluations is 1.93185165257814 and the other is .517638090205039. As suspected, one can serve as x and the other as y, as it doesn't matter if the legs are interchanged.

The arctan of the larger divided by the smaller is 75, and of course of the smaller divided by the larger is 15. Of course, to be complete, the other angle is 90.

  Posted by Charlie on 2012-07-09 12:17:43
Please log in:
Remember me:
Sign up! | Forgot password

Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (5)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Copyright © 2002 - 2018 by Animus Pactum Consulting. All rights reserved. Privacy Information