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Joint Variation
Jointly Proportional

When we say z is jointly proportional to a set of variables, it means that z is directly proportional to each variable taken one at a time.

If z varies jointly with respect to x and y, the equation will be of the form z = kxy (where k is a constant).

 

Equation: c = 5ab

Variable c is jointly proportional to a and b. That means c is directly proportional to both a and b.

Doubling a causes c to double. Doubling b causes c to double. Doubling both a and b causes c to quadruple.

a b c
1 1 5
2 1 10
1 2 10
2 2 20

 

 

See also

Inverse variation, gravity

 


  this page updated 19-jul-17
Mathwords: Terms and Formulas from Algebra I to Calculus
written, illustrated, and webmastered by Bruce Simmons
Copyright © 2000 by Bruce Simmons
All rights reserved
NCTM Web Bytes December 2004 Web Bytes March 2005 Web Bytes