[tex]\displaystyle\\\frac{x-x_A}{x_B-x_A} = \frac{y-y_A}{y_B-y_A}[/tex]
In cazul tau:
[tex]\displaystyle\\x_A = p\\y_A = q\\x_B = -q\\y_B = r[/tex]
Astfel:
[tex]\displaystyle\\\frac{x-p}{-q-p}=\frac{y-q}{r-q} \\ \\[/tex]
Se inmulteste pe diagonala si se exprima in functie de x si y. p, q si r sunt coeficienti.
[tex]\displaystyle\\(x-p) \cdot (r-q) = (y-p) \cdot (-q -p) \\\\x \cdot r - x \cdot q - p \cdot r + p \cdot q = -y \cdot q -y \cdot p + p \cdot q + p^2 \\\\x \cdot (r - q) - pr - pq = -y \cdot (q +p) + pq + p^2 \\\\x \cdot (r-q) + y \cdot (q + p) - pr - pq = pq + p^2 \\ \\x \cdot (r -q) + y \cdot (q + p) = pq + pq + pr + p^2 \\ \\x\cdot (r - q) + y \cdot (q + p) - p \cdot (2q + r + p) = 0[/tex]
