Geometry review

zee-f · 2012-12-18 12:21:05

I still get B

2×(36×pi)+603.2 = 829.39

36pi is the circle area
then the area of the triangle is= 12pi( circumference of the circle ) * (16) = 192PI or 603.2

SA = 2×(36×pi)+603.2 = 829.39

Bob · 2012-12-18 12:44:45

hi zee-f

I see what you are doing. The question is badly worded.

You have worked out (correctly)

but the question wants

The question shouldn't have the word 'total' there at all. That's just putting you off.

Of course you had the right answer part way through the calculation. How annoying! See if answer A is right. If it is, complain that the question needs re-wording so future students don't get caught out like this.

If it isn't answer A, then I don't know what is going on.

Bob

anonimnystefy · 2012-12-18 13:55:01

I think that total was put there as a reminder that a cilinder has two bases.

Bob · 2012-12-18 19:49:10

hi Stefy,

Most mathematicians use the phrase total surface area of a cylinder to mean include the two ends. That's what zee-f calculated and got it marked wrong. Most mathematicians refer to the area excluding the ends as the lateral surface area. We don't yet know if that is the answer they intended.

If it is, then asking for the total lateral surface area is confusing and it seems to me, very unfair that she lost marks when she was quite capable of calculating, and indeed had calculated, this answer.

I have encountered poor questions before on her course, such as when they asked for a estimate of the weight of a can of soup and gave as possible answers: 50 500 250 325 750 gms.

Bob

zee-f · 2012-12-19 00:27:38

So its really asking for that triangle area
2*PI*6*16=192PI
or 603.19
So A can be the answer

Last edited by zee-f (2012-12-19 00:28:38)

Bob · 2012-12-19 00:46:20

I hope so. It's hard to tell for certain because of the wording of the question.

You've tried B and that wasn't right and the other two answers don't fit the numbers at all, so I think it has got to be A.

Bob

zee-f · 2012-12-19 01:30:57

yup A was correct but I got 2 incorrect #6, #8

6. Calculate the area of the regular octagon shown.
6.B
I choose B because area = (½)(apothem)(perimeter)
1/2 * 3.8 * 48 = 91.2

8.I still think it is B I cant really find what I did incorrect for this one I really need a clue.
I used the Pythagoras to get the missing side I got 2.38 Then I used cosine= A/H 9/11 = 0.82
cos-¹ = 34.92 So that is angle A

90+34.92=124.92

So angle B = 180 - 124.92 = 55.08
A= 34.92
B= 55.08
C= 90

Bob · 2012-12-19 01:59:23

Q6. 91.2 is correct ... but it is answer C not B. see post 39.

Q8.

8.I still think it is B I cant really find what I did incorrect for this one I really need a clue.
I used the Pythagoras to get the missing side I got 2.38

It is B !!!

But quickly, once you know the missing side is 2.38 it must be opposite the smallest angle (without calculating it)

largest angle (90) is opposite the largest side (11)

middle angle (55) is opposite the middle side (9)

smallest angle (35) is opposite the smallest side (2.38)

This rule is true for all triangles.

Bob

zee-f · 2012-12-19 03:55:03

I know how annoying I said it was D because B was incorrect if thats incorrect to then I give up

zee-f · 2012-12-19 04:57:07

I answered D it was correct that was my last lesson in geometry I got a 9/10 in that lesson and still waiting for my final course grade thank you guys!!! ur always the best in helping

Bob · 2012-12-19 12:18:54

hi zee-f

Glad to help you.

But I'm puzzled.

I answered D it was correct

For which question?

Bob

zee-f · 2012-12-22 22:39:22

for #8

Bob · 2012-12-22 23:59:14

That's what I dislike about multi-choice, you did all that trigonometry, got the correct answer and had it marked wrong.

If the marker was being very pedantic and was telepathic, you did do calculations, but when a person chooses an answer you cannot tell how much working they did.

If I had been doing this question I would have done no calculations at all, got B and been very annoyed to have it marked wrong just because my marker couldn't do it 'in her head'. gggrrr

Oh well, we'll move on I guess. Is that it for math topics?

Bob

zee-f · 2013-01-07 05:08:03

yup totally agree ...... no I still need to take 1 more math course

Bob · 2013-01-07 06:29:05

OK. Good luck with it. Perhaps you'll sail thru with no help needed ... but you know where to come if otherwise.

Bob

Math Is Fun Forum

#51 2012-12-18 12:21:05

Re: Geometry review

#52 2012-12-18 12:44:45

Re: Geometry review

#53 2012-12-18 13:55:01

Re: Geometry review

#54 2012-12-18 19:49:10

Re: Geometry review

#55 2012-12-19 00:27:38

Re: Geometry review

#56 2012-12-19 00:46:20

Re: Geometry review

#57 2012-12-19 01:30:57

Re: Geometry review

#58 2012-12-19 01:59:23

Re: Geometry review

#59 2012-12-19 03:55:03

Re: Geometry review

#60 2012-12-19 04:57:07

Re: Geometry review

#61 2012-12-19 12:18:54

Re: Geometry review

#62 2012-12-22 22:39:22

Re: Geometry review

#63 2012-12-22 23:59:14

Re: Geometry review

#64 2013-01-07 05:08:03

Re: Geometry review

#65 2013-01-07 06:29:05

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