Cross-multiplication
Mathematical technique / From Wikipedia, the free encyclopedia
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Not to be confused with Cross product.
In mathematics, specifically in elementary arithmetic and elementary algebra, given an equation between two fractions or rational expressions, one can cross-multiply to simplify the equation or determine the value of a variable.
The method is also occasionally known as the "cross your heart" method because lines resembling a heart outline can be drawn to remember which things to multiply together.
Given an equation like
where b and d are not zero, one can cross-multiply to get
In Euclidean geometry the same calculation can be achieved by considering the ratios as those of similar triangles.