how to explain -1 x -1 = +1 (minus x minus equals plus). Is there any practical example (explanation) for this? I have read as a mathematical formula, but how it is true? Kindly enlighten me. Any guidance on this issue is welcome.
With advance thanks.
Let's look at, say,
We could also write this as
But we know that , so
If we want to visualise this, just picture a 10 x 10 square, and picture evaluating 9 x 9 by removing one row of 10 and one column of 10. The problem is that by doing this, one of the unit squares has been removed twice, and so needs to be put back.