I had a student tasked with summing a finite geometric sequence with |r|>1, let’s say 1+2+4+8+16. He had apparently forgotten the formula for that, but knew the formula for the infinite series a/(1-r). Good enough he thinks, and sums 1+2+4+… = -1, then subtracts off the excess terms 32+64+128+… = -32, and gets the correct answer of 31.
crwth
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Cake day: February 21st, 2026
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crwth@piefed.zipto
Ask Lemmy@lemmy.world•What nursery rhymes and playground songs were popular when you were very young?English
51·6 days agoJingle bells Jingle bells, Santa Claus is dead // GI Joe the Eskimo shot him in the head.
Row row row your boat, gently down the stream // Throw your teacher overboard and listen to her scream.
Mine eyes have seen the glory of the burning of the school // We have tortured every teacher and we’ve broken every rule.
Chinese, Japanese, Dirty knees, Look at these.
crwth@piefed.zipto
No Stupid Questions@lemmy.world•Can a puzzle with missing pieces be considered complete?English
5·11 days agoIf she’s used all the pieces and solved enough to reverse engineer the shape of all the missing pieces, then it is fully solved. If the missing pieces cannot be individually identified due to shared edges, then it is still solved, but is no longer a 1000 piece puzzle and she should only claim to have solved the 999 or 998 piece subpuzzle.

Indeed, and would have earned full marks had he said that, or even showed any awareness that his intermediate results were somehow nonstandard.