Best Answer

(a + b)/(a - b) = (c + d)/(c - d) cross multiply

(a + b)(c - d) = (a - b)(c + d)

ac - ad + bc - bd = ac + ad - bc - bd

-ad + bc = -bc + ad

-ad - ad = - bc - bc

-2ad = -2bc

ad = bc that is the product of the means equals the product of the extremes

a/b = b/c

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Q: How is a plus b over a minus b equals c plus d over c minus d?
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