Problem 1
-7+9 is the same as 9+(-7) or 9-7. All of which simplify to 2.
On the other hand, -9+7 is the same as 7+(-9) or 7-9, which simplifies to -2.
Therefore the equation -7+9 = -9+7 becomes 2 = -2, and we can see this is a false equation.
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Problem 2
Your second question has some weird typo errors going on. Please update.
