# Calculus - Algebra question

1. Feb 25, 2005

### lektor

The Numerical Values of the circumference and area of a circle add up to 16.
Determine the radius to 4 sf.

Well so far me and my friend have been working on this and all of our results have been different to the final question, :<

We first tried to manipulate with the formula pi x r^2 = a without any success, it would be appreciated if someone could clarify this question.

Yes, maybe not a very hard question but it has confused us.

Last edited: Feb 25, 2005
2. Feb 25, 2005

### Integral

Staff Emeritus
You know that the:

Area + Circumferance = 16

Area = $\pi r^2$
Circuference = $\pi r$

all you need do is solve the above relationship for r.

3. Feb 25, 2005

### danne89

Denote the area as x and the circumference as y
x + y = 16
x=Pi(y/2)^2

Then substitute y in terms of x in the second equation and solve it.

4. Feb 25, 2005

### scholar

Probably a typo, but I'm fairly sure that Circuference = $2\pi r$

5. Feb 25, 2005

### lektor

hah

Btw for thoose who are wondering the answer was 1.4683

6. Feb 25, 2005

### WORLD-HEN

why is this a "calculus-algebra" question?

7. Feb 25, 2005

### lektor

In the New Zealand Curriculum.

Caculus is comprised of

Complex numbers/algebra
Differentiation
Intergration
Conics

So by New Zealand standards this is an Calculus - Algebra question