Question

solve the formula for r
A=pi*r^2

Answer 1

@satellite73 any chance you could help me out?

Answer 2

+-sqrt(a/(pi)) = r

Answer 3

divide both sides by pi
then take the square root of both sides

Answer 4

\[\pi*r*r=A\]
\[r*r=A/pi\]

Answer 5

To get r, square root both sides.

Answer 6

dont forget the +-

Answer 7

\[\sqrt{r*r}=r= \pm \sqrt{A/\pi}\]

Answer 8

zzr0ck3r, because the radius is a length, it doesn't make sense to have a negative radius

so you don't have to worry about the plus/minus

Answer 9

we are not told this is for a circle, we are given an equation and thats it. could be for something else.

Answer 10

@henpen radius cannot be negative

Answer 11

says nothig of radius, just gives formula....

Answer 12

its good practice.

Answer 13

Why 'plus or minus': because when you square both sides back again to get r*r=A/pi, if there was a minus sign in front of the (sqrtr*r), then it would square into a plus.

Answer 14

because (-2)^2 = 2^2 = 4

Answer 15

so final answer is.. ?

Answer 16

i think i got what you are saying so far

Answer 17

in this context the final answer is -+sqrt(A/pi)

if we were talking about a circle it would not make sense to talk about a negative radius so it would be sqrt(A/pi)

Answer 18

but you said nothing about a circle or a radius...

Answer 19

okay thanks

Answer 20

the formula is for the area of a circle and nothing else - the r can only be positive

Answer 21

so is this formula only for a circle b = c*r^2??? we are given variables. we are not told they stand for anything else..... dont assume is my point, as this is math. To say a formula only works for one thing is just silly.

Answer 22

the r can only be positive once we aply it to some real world problem. but of course unless you know something I dont. A formula is a formula....not set in stone for what it is used for.

Answer 23

the r can only be positive once we apply it to some real world problem involving circles....*