Identify as inverse, direct, joint or combined. 1. y=7x. 2. xy=24. 3. f=4/r. 4. m/n=4. 5. i=2pr. 6. r=cl/r^2. 7.a=pir^2. 8.v=pir^2h.

1. y = 7x. This is an example of direct variation as the value of y also increases if the value of x is increased.
2. xy = 24. This is an example of inverse because the value of y is decreased when x is increased. 
3. F = 4/R. This is inverse variation for the same reason as number 2.
4. m/n = 4. Direct variation. For the same reason as number 1.
5. i = 2pr. Joint variation. The value of i is dependent on the values of two other variables.
6. R = cl/r². Joint variation.
7. A = pir². Direct variation. I believe pi here is for π, leaving only A being dependent only to value of r. 
8. V= pir²h. Joint variation.