25. Find the distance between the points: $A(2; -3)$ and $B(-1; 1)$; $C(-3; 4)$ and $D(5; -2)$; $O(0; 0)$ and $E(1; -4)$.
Solution. Using formulas (1) and (2), we get: the length of $AB=\sqrt{(-1-2)^{2}+[1-(-3)]^{2}}=\sqrt{25}=5$; the length of $CD=\sqrt{[5-(-3)]^{2}+(-2-4)^{2}}=\sqrt{100}=10$; the length of $OE=\sqrt{1^{2}+(-4)^{2}}=\sqrt{1+16}=\sqrt{17}$.