गुणितसमुच्चयः — Gunitasamuchyah
The product of the sum is the sum of the products. The digit sum of a product equals the digit sum of the product of the individual digit sums — a verification tool.
Why it works: Digit root is a homomorphism modulo 9: digitRoot(a×b) = digitRoot(digitRoot(a) × digitRoot(b)). This is because the digit root tracks the number modulo 9.
Speed advantage: Instant answer verification in 3 steps vs. recomputing the whole multiplication.
Best for
- Verifying multiplication, division, and squaring results
▶ See the animated lesson, practice drills & proof on SutraFlow →
Originally published at https://www.sutraflow.app/sutras/gunitasamuchyah
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