Is a proportional function f(x) = 5x linear? Why or why not? Explain with an example.

Given two variables x and y, y is directly proportional to x (x and y vary directly, or x and y are in direct variation) if there is a non-zero constant k such that

   y = kx,

The relation is often denoted, using the ∝ symbol, as

   y ∝ x

in this case k = 5/1

256π units²   (answer b)

step-by-step explanation:

the formula for the surface area of a sphere of radius r

is             a = 4πr²

and so, if r = 8 units, then the surface area is:

a = 4π(8 units)² = 256π units²   (answer b)

question:

could we have options?