PROOF WITHOUT WORDS: $a, b, c, d>0$; $ \frac{a}{b}=\frac{c}{d} \Rightarrow \frac{a}{b}=\frac{c}{d}=\frac{s a+t c}{s b+t d} $. FEJME [Internet]. 2024 Aug. 7 [cited 2026 Jan. 5];26(2):71-7. Available from: https://pphmjopenaccess.com/fejme/article/view/2033