“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} $” (2024) Far East Journal of Mathematical Education, 26(2), pp. 71–77. doi:10.17654/0973563124008.