Sjecište dijagonala $S$$S$ je polovište obiju dijagonala pravokutnika:
$$S = \frac{A + C}{2} \implies C = 2S - A$$$S = \frac{A + C}{2} \implies C = 2S - A$
$$C = (2 \cdot 3 - 1, 2 \cdot 2 - 1) = (5, 3)$$$C = (2 \cdot 3 - 1, 2 \cdot 2 - 1) = (5, 3)$

$$S = \frac{B + D}{2} \implies D = 2S - B$$$S = \frac{B + D}{2} \implies D = 2S - B$
$$D = (2 \cdot 3 - 5, 2 \cdot 2 - 1) = (1, 3)$$$D = (2 \cdot 3 - 5, 2 \cdot 2 - 1) = (1, 3)$

Ucrtavanjem točaka $C(5, 3)$$C(5, 3)$ i $D(1, 3)$$D(1, 3)$ na mrežu dovršavamo pravokutnik $ABCD$$ABCD$.