Answers:
- false
- true
- not enough
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Step-by-step explanation:
Let's say the claim is
true for any real number x. It certainly works for things like x = 5 and x = 27.
A counter-example to show this isn't true is to use x = 0.5
So,
The last statement is false, which thereby proves the original claim doesn't work for x = 0.5; by extension, the overall claim of that inequality working for any real number is false.
As you can see, all we need is one counter-example to contradict the claim to prove it false.
Unfortunately one single example is not enough evidence to prove a claim true. Think of it like saying "it's much easier to knock down a sand castle than to build it up".
Instead, we need to use a set of clearly laid out statements and reasons based on previously established theorems.