OK, I'm stupid, so explain to me why . . .

[IRLFAN]

It's claiming that R2C2 can only be 7, since 1, 2, 4, 5, 6, 8, and 9 already exist in Row 2. BUT 3 DOESN'T. So someone smarter than me tell me why R2C2 HAS to be 7. Or am I blind as well as stupid?



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[OboeWanKenoboe]

I don't know if this is how they're trying to explain it, but I see that R2C1, R2C2, and R9C2 are all either 3 or 7. This means that R9C1 can't be 3 or 7 because then the puzzle would be unsolvable. Therefore, R9C2 must be 3 (only 3 in box), so R2C2 has to be 7.