A true proportion is a mathematical equation which states that one ratio is equal to another. A true proportion will often be written in the following format: a:b = x:y in which the ratio between a and b is equal to the ratio between x and y.
Often mathematical problems will ask for proof that a proportion is true. To prove that a proportion is true, the components of the proportion can be cross-multiplied.
a:b = x:y
a/b = x/y
ay = bx
If the product of a and y is equal to the product of b and x, then the proportion is a true proportion.