1 câu trả lời
\[\begin{array}{l} gt \to (2a + 13b)(3c - 7d) = (2c + 13d)(3a - 7b)\\ \to 6ac - 14ad + 39bc - 91bd = 6ac - 14bc + 39da - 91bd\\ \to 53bc = 53ad\\ \to bc = ad\\ \to \frac{a}{b} = \frac{c}{d} \end{array}\]
\[\begin{array}{l} gt \to (2a + 13b)(3c - 7d) = (2c + 13d)(3a - 7b)\\ \to 6ac - 14ad + 39bc - 91bd = 6ac - 14bc + 39da - 91bd\\ \to 53bc = 53ad\\ \to bc = ad\\ \to \frac{a}{b} = \frac{c}{d} \end{array}\]
