 1. g_a says:

Of course, mathematics is contradictory and illogical! If you don't know her. And of course, mathematics does not exist without axioms. Just like almost everything else.

Here is the author's reasoning:

For example, 18*0=12*0.
Reducing the zeros we will have 18=12. This is illogical

Reduction is in this case a division. The division action itself can be defined by multiplication: x/y = z, which gives z*y = x. In this case, the result of division by zero is defined as a number that, when multiplied by zero, gives the original number. For example, 21/0 = ? What number do you need to multiply by zero to get 21? If we consider that when multiplied by zero, we get zero. Therefore, the result is uncertainty. For example, in JS, the value NaN is not equal to itself.

-20 = -20  > 16 – 36 = 25 – 45
4² – 4×9 = 5² – 5×9
4² – 4×9 + 81/4 = 5² – 5×9 + 81/4
(4 – 9/2)² = (5 – 9/2)²
4 – 9/2 = 5 – 9/2
4 = 5

How did you get out of this line

4² – 4×9 + 81/4 = 5² – 5×9 + 81/4

got this one

> (4 – 9/2)² = (5 – 9/2)²

???

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