Gunakasamuchyah
The factors of the sum are equal to the sum of the factors (gu · na · ka · sa · mu · cha · yah)
What it means
A second polynomial factor-check, paired with Sutra #15. Same plug-in trick — set x = 1, compare the two sides — used as a one-second self-check after any factoring step. If the factored form gives a different answer, you have a sign or coefficient error to hunt down.
Worked example
Is x² + 5x + 6 = (x + 2)(x + 3) correct? Plug x = 1. Factored form: (1+2)(1+3) = 3 × 4 = 12. Expanded form: 1 + 5 + 6 = 12. Match → factoring is correct. (If you had written (x + 1)(x + 3) by mistake, plugging in 1 would give (1+1)(1+3) = 8, instantly catching the error.)