Lesson 65 — Same-Sum Equations: When the Samuccaya Is Zero

Technique explanation

The sutra Shunyam Samyasamuccaye ("When the samuccaya is the same, that samuccaya is zero") provides an instant solution for specific rational equations. In equations of the form (x+a)/(x+b) = (x+c)/(x+d), if the sum of the numerator and denominator is the same on both sides (N1+D1 = N2+D2), that sum can be set to zero to find the root, avoiding complex cross-multiplication.

Standard fallback: Cross-multiplication, resulting in a quadratic equation (which often simplifies to linear if the x² terms cancel).

Worked examples

Example 1: Solve (x + 2)/(x + 3) = (x + 4)/(x + 1)
1. Check Samuccaya: (x + 2) + (x + 3) = 2x + 5. (x + 4) + (x + 1) = 2x + 5. They match.
2. Set to Zero: 2x + 5 = 0.
3. Solve: x = -2.5.
Result: x = -2.5
Check: Substitute x = -2.5 into the original equation: LHS = (-2.5 + 2)/(-2.5 + 3) = -0.5/0.5 = -1. RHS = (-2.5 + 4)/(-2.5 + 1) = 1.5/-1.5 = -1. Since -1 = -1, the solution is correct.

Example 2: Solve (x - 3)/(x + 5) = (x - 1)/(x + 3)
1. Check Samuccaya: (x - 3) + (x + 5) = 2x + 2. (x - 1) + (x + 3) = 2x + 2. They match.
2. Set to Zero: 2x + 2 = 0.
3. Solve: x = -1.
Result: x = -1
Check: Substitute x = -1 into the original equation: LHS = (-1 - 3)/(-1 + 5) = -4/4 = -1. RHS = (-1 - 1)/(-1 + 3) = -2/2 = -1. Since -1 = -1, the solution is correct.