Chaitanya's Random Pages

February 28, 2016

The race up the charts for two recent movies

Filed under: movies and TV — ckrao @ 7:59 pm

In recent times Jurassic World and Star Wars VII (The Force Awakens) have respectively become the fourth and third biggest movies of all time worldwide (behind Avatar and Titanic). Here is how they ranked in the all-time US/Canada charts day by day (using data from boxofficemojo.com).

 Day Jurassic World Star Wars: The Force Awakens 1 786 464 2 275 183 3 143 96 4 108 68 5 79 40 6 69 29 7 54 22 8 37 11 9 28 6 10 18 5 11 15 5 12 11 5 13 10 4 14 9 3 15 7 2 16-19 5 2 20-21 5 1 22-44 4 1 45+ 3 1

I was amazed by Jurassic World’s summer run and then that of The Force Awakens simply blew my mind. 🙂

February 27, 2016

Cutting a triangle in half

Filed under: mathematics — ckrao @ 9:40 pm

Here is a cute triangle result that I’m surprised I had not known previously. If we are given a point on one of the sides of a triangle, how do we find a line through the triangle that cuts its area in half?

Clearly if that point is either a midpoint or one of the vertices, the answer is a median of the triangle. A median cuts a triangle in half since the two pieces have the same length side and equal height.

So what if the point is not a midpoint or a vertex? Referring to the diagram below, if $P$ is our desired point closer to $A$ than $B$, the end point $Q$ of the area-bisecting segment would need to be on side $BC$ so that area(BPQ) = area(ABC)/2.

In other words, we require area(BPQ) = area(BDQ), or, subtracting the areas of triangle BDQ from both sides,

$\displaystyle |DPQ| = |DCQ|.$

Since these two triangles share the common base $DQ$, this tells us that we require them to have the same height. In other words, we require $CP$ to be parallel to $DQ$. This tells us how to construct the point $Q$ given $P$ on $AB$:

1. Construct the midpoint D of $AB$.
2. Draw $DQ$ parallel to $AP$.

See [1] for an animation of this construction.

In turns out that the set of all area-bisecting lines are tangent to three hyperbolas and enclose a deltoid of area $(3/4)\ln(2) - 1/2 \approx 0.01986$ times the original triangle. [2,3,4]

References

[1] Jaime Rangel-Mondragon, “Bisecting a Triangle” http://demonstrations.wolfram.com/BisectingATriangle/ from the Wolfram Demonstrations Project Published: July 10, 2013

[4] Henry Bottomley, Area bisectors of a triangle, January 2002

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