Question

What is the radius for the circle given by the equation x^2+(y-3)^2=21? Round your answer to the nearest thousandth.

Answer 1

do you know the equation of a circle ?

Answer 2

No, do you mind helping me out with that?

Answer 3

see
http://www.mathsisfun.com/algebra/circle-equations.html
and scroll down to see the equation

Answer 4

can you write down the equation of a circle ?

Answer 5

(x-a)^2+(y-b)^2-r^2. is that correct?

Answer 6

(x-a)^2+(y-b)^2=r^2; correct one
a,b are the coordinates of its center and r is radius so just compare those two equations

Answer 7

How do I find the radius and coordinates though?

Answer 8

comparison of thq eqn in given ques and the the eqn above

Answer 9

Sooo 0 and 3 would be coordinates and 21 is the radius?

Answer 10

noo...rt21 is the radius as 21=r^2

Answer 11

okay, so square root of 21?

Answer 12

yep

Answer 13

But it says "Round your answer to the nearest thousandth." how am I supposed to do that?

Answer 14

use calculator or ancient way to find root

Answer 15

I got 4.58257569... so would the answer be 4.59?

Answer 16

the thousandth digit is the third digit to the right of the decimal point
look at the 4th digit to the right. if smaller than 5, just keep the 3 digits as is
if the the 4th digit is 5 or more, add 1 to the 3rd digit.

Answer 17

thousands got 3 digits so 4.523

Answer 18

wouldn't it be 4.583?

Answer 19

yes

Answer 20

thank you! :)