Question

A right circular cylinder has a base whose area is 154 square feet. If the height of the cylinder is 19 feet, what is its lateral area? Use π = 22 over 7

1980 ft2

836 ft2

990 ft2

1672 ft2

Answer 1

Figure the radius from the area of the base, first.

Answer 2

Can you?

Answer 3

no can you explain how?

Answer 4

What is the area of a circle, it's the same.. (this is a cylinder).

Answer 5

ughh this is mkn my head hurt . im sorry ive took 4 exams today so far .

Answer 6

Area = π × r2

Answer 7

So 154 = 22/7 times r^2
What is r?

Answer 8

to find that wud i half to multiply 22/7 * 154 then divide by 2?

Answer 9

Not quite.
sqrt(154 times 7/22)

Answer 10

so it wud be 154 * 22/7 which is 484 then square it ? so it wud be 484^2 ?

Answer 11

reread

Answer 12

im sorry i dont get it . :/

Answer 13

You multiplied by 22/7 instead of 7/22

Answer 14

ok i got 49.

Answer 15

OK, now what?

Answer 16

Tell you what, let's go step by step, OK?

Answer 17

yes please.

Answer 18

We have
pi r^2 = 154 = (22/7) r^2
OK?

Answer 19

yes

Answer 20

So multiply both sides by 7
7 x 154 = 22 r^2

Answer 21

(7 x 154)/22 = r^2
OK?

Answer 22

yes

Answer 23

Now do the multiplication, then take the square root of both sides

Answer 24

The 49 is what you got before, but you need the square root.

Answer 25

so next would be 1,078/22=r^2
then its 49=r^2
then 49^2
n that is 2,401

Answer 26

square root

Answer 27

ooohh sorry . its 7

Answer 28

Yes! So r = 7. OK?

Answer 29

yes.

Answer 30

The other part of the problem is to find the "lateral area", the area of the "skin" on the cyclinder (not counting the ends), like an open tube.

Answer 31

There's a formula for that, but I want you to visualize sliding a rubber band down the length of the cylinder. Can you see that?

Answer 32

yes

Answer 33

The area the rubber band will cover is the perimeter of the circle (length of the rubber band) times how far we roll it

Answer 34

So the formula is 2 pi r times the height of the cylinder.

Answer 35

ok . so tht wud be 836

Answer 36

2 * 22/7 * 7 * 19 = 836

Answer 37

Sounds good to me.

Answer 38

thank you soooo much . you helped me soo much

Answer 39

yw