Alphabeta Math
TheoremStatement: Literature-sourcedProof: Literature-sourcedSession-authored (Fable 5 assisted)precheck passaudited 2026-08-11
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  • Literature-sourced: the exact statement appears in a cited source; only wording and notation differ.
  • AI-adapted: a semantically identical restatement of literature-sourced material, modulo indexing, notation, and boundary cases adopted by the library.
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Over an integral domain, degrees add under multiplication of nonzero polynomials

Statement

If RR is an integral domain and f,gR[x]f,g\in R[x] are nonzero, then fg0fg\ne0 and

deg(fg)=degf+degg,lc(fg)=lc(f)lc(g).\deg(fg)=\deg f+\deg g,\qquad \operatorname{lc}(fg)=\operatorname{lc}(f)\operatorname{lc}(g).

Facts & Assumptions

Given: An integral domain RR and nonzero polynomials f,gR[x]f,g\in R[x].

[L1]

The coefficient of degree degf+degg\deg f+\deg g in fgfg is the product of the two leading coefficients, and all higher coefficients vanish (Degree inequalities for sums and products over a commutative ring).

[L2]

In an integral domain, a product of two nonzero elements is nonzero (Zero divisor, and integral domain: a commutative ring with 101 \ne 0 and no zero divisors).

Proof

technique · direct
1.1

The leading coefficients of ff and gg are nonzero, so [L2] makes their product nonzero.

givenL2
2.1

Fact [L1] identifies that product as the coefficient at degree degf+degg\deg f+\deg g and makes every higher coefficient zero, so fg0fg\ne0, its degree is the sum of the degrees, and its leading coefficient is the product of the leading coefficients.

step 1.1L1

Depends on

Used by

Dependency tree · next 3 levels

Direct dependencies and their dependencies through the next three levels: 17 results over 12 levels. An arrow runs from a result to what uses it, and this result sits at the bottom with a heavier outline. Click the chart to enlarge it.

Sources