Question

What is the inverse to: If a figure is a Pentagon then it has 5 sides?​

Answer 1

2f(n)=3n2−n,

multiply both sides by 12. We get

24f(n)=36n2−12n.

Note that 36n2−12n=(6n−1)2−1.

We get (6n−1)2=24f(n)+1,

then 6n−1=24f(n)+1−−−−−−−−−√,

then 6n=24f(n)+1−−−−−−−−−√+1.

Answer 2

You simply reverse the conditional. So for example it would be:

If a figure is not a pentagon, it does not have five sides.