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College+ · Number Theory

Divisibility & the Euclidean algorithm

125 problems in this skill, each with a solver-verified answer key. Answers are checked the moment you submit — with a hint if you want one and a worked solution afterwards.

What the problems look like

A few statements from this skill. Answers, hints and worked solutions live in the practice session.

  1. Warm-up

    Bezout's identity guarantees integers x,yx,y with ax+by=gcd⁡(a,b)ax+by=\gcd(a,b). For a=18a=18 and b=21b=21, the extended Euclidean algorithm yields x=−1x=-1 and y=1y=1. Evaluate the Bezout combination a(−1)+b(1)a(-1)+b(1), which equals gcd⁡(a,b)\gcd(a,b).

  2. Warm-up

    Bezout's identity guarantees integers x,yx,y with ax+by=gcd⁡(a,b)ax+by=\gcd(a,b). For a=18a=18 and b=24b=24, the extended Euclidean algorithm yields x=−1x=-1 and y=1y=1. Evaluate the Bezout combination a(−1)+b(1)a(-1)+b(1), which equals gcd⁡(a,b)\gcd(a,b).

  3. Warm-up

    Bezout's identity guarantees integers x,yx,y with ax+by=gcd⁡(a,b)ax+by=\gcd(a,b). For a=24a=24 and b=28b=28, the extended Euclidean algorithm yields x=−1x=-1 and y=1y=1. Evaluate the Bezout combination a(−1)+b(1)a(-1)+b(1), which equals gcd⁡(a,b)\gcd(a,b).

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