Question

Which of the following correctly describes the variation in the equation A = πr2?

1. A varies directly with r.
 2. A varies jointly with π and r.
 3. A varies inversely with r.
 4. A varies directly with π and r.

Answer 1

The answer is A because A varies directly with the radius.

Answer 2

Option 1 is correct

A varies directly with r.

Explanation:

The direct variation says that:

`y \propto x`

then the equation is in the form of:

`y = kx`

where, k is the constant of variation

Given the equation:

`A = \pi r^2`

Here,
`\pi` is constant in the equation.

By above definition we have;

`A \propto r`

Therefore, the following correctly describes the variation in the given equation is,

A varies directly with r.