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For which $x\in\mathbb{R}$ does $\neg(3x>21\implies x\leq 5)$ hold?

I believe it holds for all $x>7$, but I don't know how to formally write this down.

Can someone help me out? Is there a systematic way of doing this?

Git Gud
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james
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1 Answers1

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your statement is equivalent to $$ \neg((x \gt 7)\implies \neg (x\gt 5)) $$ since $\neg(a \implies b) \equiv \neg(\neg a \lor b) \equiv a \land \neg b$ if you substitute the expressions you will see that your belief is well-founded

David Holden
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