**Definition of Jointly Proportional **

- If a variable z is jointly proportional to a set of variable x and y, the z = kxy, where k is the constant of proportionality.

* ***More about Jointly Proportional**

- Jointly proportional is also known as joint variation.

**Example of Jointly Proportional **

- The kinetic energy, E, of a moving object is jointly proportional to its mass, m, and the square of its speed, v.i.e., E = k .m. v
^{2}

**Solved Example on Jointly Proportional**

If x is jointly Proportional to y and z when x = 4, y = 8 and z = 9, then find the value of x when y = 2 and z = 18.

Choices:

A. 1

B. 0

C. 2

D. 4

Correct Answer: C

Solution:

Step 1:x a k. y. z [joint proportional]

Step 2:x = k. y. z

Step 3:4 = k. 8. 9 [Substituting the values for x, y, z.]

Step 4:k = [Simplify.]

Step 5:Therefore, x =. 2. 18 [Substituting the values for k, y and z in x = k. y. z]

Step 6:So, x = 2 [Simplify.]

**Related Terms for Jointly Proportional**

- Constant of proportionality
- Direct proportional
- Variables