Question

the ratio between the circumference of two circles is 4:9,find the ratio between their areas.

Answer 1

@mathmath333

Answer 2

\(\large\tt \begin{align} \color{black}{

2\pi ~oa=4k\\~\\

2\pi ~ob=9k\\~\\

\dfrac{oa}{ob}=\dfrac{4}{9}\\~\\
\dfrac{oa^2}{ob^2}=\dfrac{16}{81}\\~\\
\dfrac{\pi ~oa^2}{\pi ~ob^2}=\dfrac{16}{81}\\~\\



}\end{align}\)

Answer 3

?

Answer 4

what is formula for area of circle ?

Answer 5

pi^r^2

Answer 6

it is \(\pi~r^2\) right

Answer 7

yes

Answer 8

what is formula for circumference of circle

Answer 9

2^pi^r

Answer 10

u mean \(2\pi r\)

Answer 11

yes

Answer 12

yes

Answer 13

so


\(\dfrac{2\pi r_1}{2\pi r_2}=\dfrac{4}{9}\) is given , u agree

Answer 14

so

\(\dfrac{ r_1}{r_2}=\dfrac{4}{9}\) u agree

Answer 15

yep

Answer 16

so

\(\dfrac{ r_1^2}{r_2^2}=\dfrac{16}{81}\) u stilll agree

Answer 17

yes

Answer 18

ok

\(\dfrac{ \pi r_1^2}{\pi r_2^2}=\dfrac{16}{81}\)


still yes

Answer 19

yes

Answer 20

ok

\(\dfrac{A_1}{A_2}=\dfrac{\pi r_1^2}{\pi r_2^2}\)


still yes

Answer 21

yes

Answer 22

what is \(A_1\) and \(A_2\)

Answer 23

16/81?

Answer 24

yes

Answer 25

now?

Answer 26

these are the ratio of the areas,u wanted to find .lol

Answer 27

one more question

Answer 28

ok

Answer 29

the wheel of a cart is making 5 revolutions per sec . if the diameter of the wheel is 84cm find the speed in kn/hr give ur answer in the correct nearest km

Answer 30

u mean speed in km/hr ?

Answer 31

yes that was a typo i need it in km/hr.

Answer 32

help?

Answer 33

what is circumference of the wheel

Answer 34

44 x 6?

Answer 35

\(\huge C=2\pi r=\pi d\)

Answer 36

orry its 22 x 12

Answer 37

sorry

Answer 38

264cm?

Answer 39

\(C=\pi d=\dfrac{22}{7}\times 84 \)

Answer 40

yes

Answer 41

now?

Answer 42

so one revolution means it travels 264 cm , u agree

Answer 43

yes

Answer 44

so how much distance it travels in one second

Answer 45

264cm

Answer 46

the wheel of a cart is making 5 revolutions per sec
^
given in question

Answer 47

1 revolution =264 cm

5 revolution =?

Answer 48

1320?

Answer 49

1320cm?

Answer 50

yes but it is given in unit \(\dfrac{cm}{sec}\)

u want it in \(\dfrac{km}{hr}\)

Answer 51

0.0132km

Answer 52

1cm =...km ?

Answer 53

yes

Answer 54

thats the answer?

Answer 55

1 sec= .. . hr?

Answer 56

3600

Answer 57

u mean 1 sec =3600 hrs ??

Answer 58

i meant 1 hr = 3600 secs

Answer 59

so 1 sec = ..hrs?

Answer 60

idk

Answer 61

\(1~sec=\dfrac{1}{3600} hrs\) u agree

Answer 62

\(1~hr =3600~seconds\) divide both sides by \(3600\) what will u get

Answer 63

0.00027?

Answer 64

0.00027hr?

Answer 65

yes

Answer 66

so \(\dfrac{0.0132}{0.00027}\)=

Answer 67

idk

Answer 68

http://www.wolframalpha.com/input/?i=%5Cdfrac%7B0.0132%7D%7B0.00027%7D

Answer 69

so it is \(\approx\dfrac{48~km}{hr}\)

Answer 70

thx,i hv more q's

Answer 71

Another way to look at the first question:

Theorem:
If two plane figures are similar, the square of the scale factor of the two figures is equal to the ratio of any two corresponding area measurements of the figures.

All circles are similar.
Circumference is linear.

(4/9)^2 = ratio of areas

16/81 = ratio of areas of the two circles.