"Why does the graph of y2=1−(4x^10^12)/(pi2) look so much like a square? I want to know why the equation y2=1−(4x^10^12)/(pi2) gives an approximate square.

Abdiel Mays

Abdiel Mays

Answered question

2022-11-08

I want to know why the equation y 2 = 1 4 x 10 12 π 2 gives an approximate square.
Background
I was just playing around with functions and I wanted to see if y = | sin ( π x 2 ) | (radians) would give a semicircle for the interval [0,2] as the distance of (1,0) is the same from (0,0), (2,0) and (1,1), all of which will lie on the curve. The equation of a unit semicircle with its centre at (1,0) is y = 2 x x 2
I know that the curves of both the equations don't resemble each other much but I still thought of approximating the sine function using this because I thought that it could still be combined with another approximation to make a better approximation. Anyway, I did it and for ϕ = x   r a d i a n s , the value of sinϕ can to be approximately 2 π π x x 2 . It looked like a semi-ellipse and so I verified it to find that it was a semi-ellipse. I thought of using this to derive the equation for an ellipse with it's centre at the origin and the value of a and b being π 2 and 1 respectively.
The equation came out to be : y 2 = 1 4 x 10 12 π 2
Finally, I thought of playing with this equation and changed the exponent of x. I observed that as I increased the power, keeping it even, the figure got closer and closer to a square.
y 2 = 1 4 x 10 12 π 2 gave a good approximation of a square. For the exponent of x being some power of 10 greater than 1012, a part of the curve began to disappear.

Answer & Explanation

cenjene9gw

cenjene9gw

Beginner2022-11-09Added 13 answers

First, let's determine the possible values for x.
Since y 2 is non-negative, we have:
1 4 x 10 12 π 2 0
x 10 12 π 2 4
( π 2 4 ) 10 12 x ( π 2 4 ) 10 12
1.0000000000009031654105793 x 1.0000000000009031654105793
For the decimal approximation used above, see this WolframAlpha computation.
Note that for x = ± ( π 2 4 ) 10 12 = def ± β , we have y 2 = 0 , and hence y=0.
When x = ± 0.999999 , we find that y 2 1 10 434 , 000 and y ± ( 1 10 217 , 000 ) . The table below shows the result of several similar calculations.
x y 2 y 0 1 ± 1 ± 0.9 1 10 45 , 700 , 000 , 000 ± ( 1 10 22 , 900 , 000 , 000 ) ± ( 1 10 6 ) = ± 0.999999 1 10 434 , 000 ± ( 1 10 217 , 000 ) ± ( 1 10 10 ) = ± 0.9999999999 1 2.5 × 10 44 ± ( 1 1.2 × 10 22 ) ± ( 1 10 12 ) 0.8509 ± 0.9224 ± ( 1 10 15 ) 0.5951 ± 0.7714 ± 1 0.5947 ± 0.7711 ± 1.000000000000903 0.000165 ± 0.012860 ± β 0 0
Thus, using the fact that y 2 is a decreasing function of | x | for β < x < β , it follows that the points (x,y) on the graph form two nearly horizonal arcs and two nearly vertical arcs. The upper arc is concave down, has endpoints ( β , 0 ) and ( β , 0 ) ,, reaches a maximum height above the x-axis at the point (0,1), and visually it will look like a horizontal segment for β 1 < x < 1 β along with a pair of vertical segments, one at x = 1 β and the other at x = 1 β .. The lower arc is the reflection of the upper arc about the x-axis.
Visually, the upper arc will look like the upper horizontal and two vertical sides of a rectangle whose vertices are (−1,0) and (−1,1) and (1,1) and (1,0). Visually, the lower arc will look like the lower horizontal and two vertical sides of a rectangle whose vertices are (−1,−1) and (−1,0) and (1,0) and (1,−1). Together, these two arcs will visually look like the four sides of a square whose vertices are (−1,−1) and (−1,1) and (1,1) and (1,−1).

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