Context: Playing Lost Mines of Phandelven with a group of friends online. We were about to get fireballed
Langlock: I cast counterspell
DM: Well, it won’t work because you only have a sixty foot range. This guy is fifty feet away and thirty feet up.
Me: Wait, hold on, hold on. Gotta check something real quick, what is 50 squared plus 30 squared!?
*Cue the party quickly using Pythagorean theorum in order to prove that he is within range*
Considious: 58.309! He is within range
DM, clearly defeated: Alright, well. You cast counterspell and stop what you recognize as a fireball
*Cue everyone making sighs of relief and surprise*
Me: Langlock is the MVP
Considious: Phew, we dodged a TPK
Me (Red Dragonborn Paladin) Well, you all might have died. I would have been fine.