How can X-1 be equal to X-1

x^1-1=x-1
x^2-x=0
x(x-1)=0
X = 0 or x = 1
That is: when x = 1 or x = 1, x ^ 2-1 equals X-1

3.4.6.7.8.9.10. In the nine squares, the sum of each horizontal, oblique and vertical row is equal to 21

What you want should be
411 6
9 7 5
8 310
The sum of horizontal, oblique and vertical lines is 21

How fast is memory from 11 square to 25 square

Memorize

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