Suppose x, y and z represent three quantities. When a variable quantity is proportional to the product of two or more variables, we say that it varies jointly. For example, the equation y = kxz means that y varies jointly with x and z. When direct and inverse happen at the same time it is called combined variation.
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Suppose x, y and z represent three quantities. When a variable quantity is proportional to the product of two or more variables, we say that it varies jointly. For example, the equation y = kxz means that y varies jointly with x and z. When direct and inverse happen at the same time it is called combined variation.
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