Definition:Compound Ratio
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Definition
Let $R_1 = a : b$ and $R_2 = c : d$ be ratios.
The compound ratio of $R_1$ and $R_2$ is defined as:
- $R_1 R_2 = a c : b d$
That is, it is the product of the two ratios.
Historical Note
Euclid never formally defined a compound ratio, but instead referred to a ratio compounded of two ratios.
In the words of Euclid:
- Equiangular parallelograms have to one another the ratio compounded of the ratios of their sides.