Here is an example of verbal_symbolic-only reasoning.
Definition of Circle
Definition: A circle is the set of all points that are the same distance, r, from a fixed point.
General Formula: X2 + Y2 = r2 where r is the radius.
According to this verbal_symbolic-only reasoning, we still have a circle even if r=0 or r=∞, which is simply nonsense.
The way you convey your thoughts about the circle strongly suggests that you never attempted to draw one using other means than a compass. Here are a few arguments that tend to support my claim.
Start with the implicit equation that defines the unit circle:
x
2 + y
2 = 1
The presence of
x and
y in the equation tells you that the circle will be drawn with the help of Cartesian coordinates and the equation assumes that the center of the unit circle is at
x=0 and
y=0. The presence of both variables also tells you that it is a function that will draw the circle.
Since
1 = 12, you can rewrite the equation this way:
x
2 + y
2 = 1
2
A "unit circle" means that the radius of it equals 1, or
r = 1. That definition rewrites the above equation to the form that you presented:
x
2 + y
2 = r
2
You see (or you should) that the equation strongly resembles Pythagorean theorem. Just consider the radius as the hypothenuse of the right-angle triangle where the hypothenuse has a constant length (h =1). Now call upon your visual_spatial brain skills to see how the circle will be drawn.
The pic shows a circle with
r = 2.. Since the implicit equation cannot do the job of drawing the circle, you need to convert it into its explicit form to separate the independent variable
x from the dependent variable
y. You will basically compute the length of the y-side of the right-angle triangle within the circle according to the given x-side whose length varies.
y = √(r
2 - x
2)
The function f(x) = y will draw a set of points where the set is defined as Semicircle. (You can't draw a full circle using only one function in the Cartesian coordinate system.)
Now here is once again your assertion:
General Formula: X^2 + Y^2 = r^2 where r is the radius.
According to this verbal_symbolic-only reasoning, we still have a circle even if r=0 or r=∞, which is simply nonsense.
Since
r=∞ is an illegal definition given the way you wrote the implicit equation, you can use the other option, where the radius is zero, and do the substitution within the function (
r2 = 02 = 0).
y = √(0 - x
2) = √(- x
2)
Remember that
- x2 = - (x2). Since there is no real result to the square root of any negative number, the circle cannot be drawn when
r=0.
In other words, "we still have a circle" NOT. That's how math works: just follow the rules and hope for the best.
But when Man decides that he wants that circle, he will have it no matter what. There is a magic letter that can be added to the equation where the radius is zero and the circle will exist pretty, even though it actually doesn't exist on a differently defined plane - the one that is closer to the real world around us. What is the magic letter that you stick into the function right after the
x, Doron?
Here is a clue: the magic letter is the first in a word that describes your attitude toward simple proofs the best.