Using k as the constant of proportionality, write an equation that expresses: z varies jointly as x and y.

z= kxy

Step-by-step explanation:

There are three types of variation. We have direct, inverse and joint.

Variation has to do with the manner in which we relate two mor more variables either directly or inversely.

For joint variation, we relate two or more variables to one another. A variable among those variables is written in terms of the remaining variables directly.

According to the question, since we have three variables z, x and y and we are to express z joint as x and y.

Joint variation is a "direct relationship" between variables i.e z will be directly proportional to the product of x and y making k as constant of proportionality. Mathematical relationship will give us;

Z=kxy

answer: 25.4 units

step-by-step explanation: radius = 12.7 units

diameter = twice the radius

diameter = 12.7 x 2

= 25.4