Given mn is the median of parallelogram ijkl, and the bases of parallelogram ijkl are 10m, find the length of mn.

a. 5m
b. 10m
c. 20m
d. 50m

Inverse Variation

Inverse Variation

The statement "y varies inversely as x means that when x increases, ydecreases by the same factor. In other words, the expression xy is constant:

xy = k    

where k is the constant of variation.

We can also express the relationship between x and y as:

y =      

where k is the constant of variation.

Since k is constant, we can find k given any point by multiplying the x-coordinate by the y-coordinate. For example, if y varies inversely as x, and x = 5 when y = 2, then the constant of variation is k = xy = 5(2) = 10. Thus, the equation describing this inverse variation is xy = 10 or y = .

Example 1: If y varies inversely as x, and y = 6 when x = , write an equation describing this inverse variation.

k = (6) = 8  

xy = 8 or y =  

Example 2: If y varies inversely as x, and the constant of variation is k = , what is y when x = 10?

xy =  

10y =  

y = × = × =  

k is constant. Thus, given any two points (x1, y1) and (x2, y2) which satisfy the inverse variation, x1y1 = k and x2y2 = k. Consequently, x1y1 = x2y2 for any two points that satisfy the inverse variation.

Example 3: If y varies inversely as x, and y = 10 when x = 6, then what is y when x = 15?

x1y1 = x2y2  

6(10) = 15y  

60 = 15y  

y = 4  

Thus, when x = 6, y = 4.