In proportions, the product obtained by multiplying the numerator of one ratio by the denominator of another ratio. When two ratios are equal, their cross products are equal, providing a method for solving proportions.
The term 'cross' refers to the X-shaped pattern created when drawing lines between the numbers being multiplied across the proportion. This visual representation and terminology became standard in algebra textbooks during the 19th century.
Cross products are like mathematical DNA matching - they reveal whether two ratios are truly equivalent! This elegant technique transforms proportion problems into simple equations, making it one of the most powerful tools in applied mathematics and real-world problem solving.
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