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x over a cubic binomial beside the root of another is integrated at the third elementary ratio - #1862

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Rafael-SOWNet merged 2 commits into
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the-third-elementary-ratio-of-x-over-two-cubic-binomials
Oct 12, 2026
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Rafael-SOWNet merged 2 commits into
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the-third-elementary-ratio-of-x-over-two-cubic-binomials

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Part of #718.

x/((a + b x^3) sqrt(c + d x^3)) is elementary at three ratios, and the integrator knew two of them (#1790). This adds the third, a^2 d^2 - 20 a b c d - 8 b^2 c^2 = 0, Rubi's rules 57 and 58 in 1.1.3.4. Here r = (a d - 10 b c)/(6 b c) is sqrt(3) or -sqrt(3). The antiderivative has two arctangents and two inverse hyperbolic tangents in s = sqrt(c r), and they swap places when c r < 0. So the answer is split by that sign, and each branch is real.

Measured on master f009b5d and on this branch (net10.0, Integrate("x")):

Input master 2.5.0 this branch
x/((b*x^3+2*a*(5+3*sqrt(3)))*sqrt(a+b*x^3)) and its three sign variants unevaluated unevaluated 1,663–1,711 characters
x/((b*x^3+2*a*(5-3*sqrt(3)))*sqrt(a+b*x^3)) and its three sign variants unevaluated unevaluated 1,703–1,753 characters
Welz 173–176, e.g. x/((10+x^3+6*sqrt(3))*sqrt(1+x^3)) unevaluated unevaluated 626–656 characters
control x/((4-x^3)*sqrt(1-x^3)) 358 — 358
control x/((8-d*x^3)*sqrt(1+d*x^3)) 313 — 313

The corpus was run with both arms on master f009b5d. Every family is unchanged except for these 12 rows, which go from unevaluated to solved, with 0 wrong and 0 errors. 1.1.3.4:857 and 4.1.7:286 also moved, but they sit at the time limit and the changed code returns immediately for them. The gate passed, and the suite passed 15,282 tests. The unit test gains five rows, at both signs of c and both signs of r.

🤖 Generated with Claude Code

https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura

Rafael-SOWNet and others added 2 commits October 12, 2026 19:52
…he third elementary ratio

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura
…e breaking changes

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura
@Rafael-SOWNet Rafael-SOWNet added this to the 2.6.0 milestone Oct 12, 2026
@Rafael-SOWNet
Rafael-SOWNet merged commit c267991 into master Oct 12, 2026
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@Rafael-SOWNet
Rafael-SOWNet deleted the the-third-elementary-ratio-of-x-over-two-cubic-binomials branch October 12, 2026 22:17
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