How Do You Find the Radius When a Circle's Area and Circumference Total 16?

[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.

 

[Integral]

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.

 

[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.

 

[scholar]

Circuference = \pi r

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

 

[lektor]

hah

we had actually already got it, but we messed up the quadractic formula calculation.

Btw for thoose who are wondering the answer was 1.4683

 

[WORLD-HEN]

why is this a "calculus-algebra" question?

 

[lektor]

why is this a "calculus-algebra" question?

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