Above is not an valid proof because a proof cannot start with the proposition, no matter what.
You can also prove by cases, stating that when
x=0 and when
x>0. (problem 2)
You can cite other proves by using "by" word (problem 3)
You can prove by double prove (greater than, smaller than) (problem 4)
:warning: You have to say the left is what, the right is what, and the left = right. (problem.1)
:warning: You cannot
Let the thing we are trying to prove.
:warning: some operations are irreversible. (like
sqrt(x^2)=|x|) and you cannot remove absolute value from both side. (problem )
Sometimes derivatives lose information :question: why?
:question: you cannot remove absolute value from both side? TODO: do all problems
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