It's not always the case, but often verifying an answer is far easier than coming up with the answer in the first place. That's precisely the principle behind the RSA algorithm for cryptography.

Sure, it's easy to check ((sqrt(x-3)+1)/(x/8)) is less than 4. Now do it without calculus.

Very much like this effect https://www.reddit.com/r/opticalillusions/comments/1cedtcp/s... . Shouldn't hide complexity under a truth value.