What is the primary result of cross-multiplication in a proportion?

What is the primary result of cross-multiplication in a proportion?

• A. ad = bc.
• B. The fractions are added.
• C. The terms are rearranged to compare numerators.
• D. The proportion becomes undefined.

Answer: (A)

Cross-multiplication in a proportion starts from the idea that two fractions are equal. If a/b = c/d with nonzero b and d, multiply both sides by b d to clear the denominators. This yields a d = b c. In other words, the products of the outer and inner terms are equal, which is the practical result you use to solve for any unknown. For example, 3/4 = x/8 leads to 3×8 = 4x, so x = 6. This isn’t about adding fractions or rearranging terms; it’s about equating the cross products. If a denominator were zero, the original proportion wouldn’t be valid, so the cross-multiplication step wouldn’t apply.

Cross-multiplication in a proportion starts from the idea that two fractions are equal. If a/b = c/d with nonzero b and d, multiply both sides by b d to clear the denominators. This yields a d = b c. In other words, the products of the outer and inner terms are equal, which is the practical result you use to solve for any unknown. For example, 3/4 = x/8 leads to 3×8 = 4x, so x = 6. This isn’t about adding fractions or rearranging terms; it’s about equating the cross products. If a denominator were zero, the original proportion wouldn’t be valid, so the cross-multiplication step wouldn’t apply.