# Concept derivation guides

299 concept teaching guides, separate from the 36,000 individual question derivations.

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Concept guide



## [Euclid and back-substitution for signed inputs](/en/derivations/derivation-mko-euclidean-algorithm-01/?from=%2Fen%2Fderivations%2F%3Fq%3Dmko-euclidean-algorithm)

gcd(-84,30)=6, with (-84)*1+30*3=6.

Euclidean algorithm

derivation-mko-euclidean-algorithm-01





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