Question

The diameter of a circle is 16cm By what amount must the radius be decreased in order to decrease the area by 48pi square centimeters. (i have to solve it using applications of equations)

Answer 1

area = pi*d/4

Answer 2

area = pi*(d^2)/4

Answer 3

sry...

Answer 4

how did you get this?

Answer 5

that is just the equation for the area of a circle..

Answer 6

so to decrease the area...

Answer 7

i understand that, but how do i get waht number the radius decreases by?

Answer 8

two equations

Answer 9

area = pi*(16^2)/4
area -48pi = pi*(16^2)/4

Answer 10

pi*(256/4)-48pi

Answer 11

area -48pi = 64pi - 48 pi

Answer 12

area - 48pi = 16pi

Answer 13

16pi is your answer

Answer 14

ugh im so confused :( i wish my teacher would acctually teach me stuff

Answer 15

ok.. so lets backup

Answer 16

grab a beer.. lets go...

Answer 17

start with the equation of a circle

Answer 18

area = pi (d^2/4)

Answer 19

X 2 + Y 2=r2?

Answer 20

now, both side are in "area" units...

Answer 21

yes, that is the equation of a circle.. i meant the equation for the area fo a circle..

Answer 22

area = pi (d^2/4)

Answer 23

oh A= pi(r2)

Answer 24

start with that guy

Answer 25

yeah we can use that one too

Answer 26

area = pi * r^2

Answer 27

subtract from both side the area you want to change

Answer 28

so A= pi(8^2)

Answer 29

area -48pi = pi (8^2)-48pi

Answer 30

yes

Answer 31

oh i get since we know the area we put it out front

Answer 32

kinda.. we know what area we want to subtract... to we can put that on both sides of the equation without changing anything

Answer 33

so break down that equation...

Answer 34

area -48pi = 64pi -48pi

Answer 35

then add thos together to get 16pi?

Answer 36

yup

Answer 37

then add 48 to both sides?

Answer 38

now what radius gives you 16pi

Answer 39

4

Answer 40

pi r^2

Answer 41

sqrt of 16 is 4

Answer 42

easy peasy

Answer 43

oh okay thanks i get it

Answer 44

although im not sure how to put that in the way she wants us to write it

Answer 45

that was always my problem too... i got the answers... just the work was never there..