Math Is Fun Forum

otherwiseknownaskyra

Member

Registered: 2014-04-08

Posts: 13

Geometry

I submitted my answers to my teacher through my online course and got 18/20 correct!
But I would like to have 20/20 correct so here are the ones I missed:

7. The apothem of a regular 9-sided figure is 6 feet and the area is 117.67 square feet. What is the perimeter of the regular 9-sided figure?   

A 4.36 feet
B 19.61 feet
C 39.22 feet
D 54.00 feet

I did A=bh
117.67=b(6)
19.61=b
My answer was B and it was marked incorrect.

18. In the diagram shown, a 12-foot slide is attached to a swing set. The slide makes a 65 degree angle with the swing set. Which answer most closely represents the height of the top of the slide?

A 5.0 feet
B 5.6 feet
C 10.9 feet
D 25.7 feet

I didn't know how to do this one so I guessed B which was wrong

Thank you for the help!

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Making mistakes is a lot better than not doing anything. -Billie Joe Armstrong

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Geometry

Hi;

Doing a quick and rough check, B for the first one is incorrect. The answer is C.

For the second one answer A is correct. You would use SOHCAHTOA for this one.

Please recheck you calculations and welcome to the forum.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

otherwiseknownaskyra

Member

Registered: 2014-04-08

Posts: 13

Re: Geometry

7. I know B is incorrect, but I'm not sure how I'm supposed to end up with C.

18. In the diagram shown, a 12-foot slide is attached to a swing set. The slide makes a 65 degree angle with the swing set. Which answer most closely represents the height of the top of the slide?

cos(65)=x/12
0.423=x/12
5.076=x

That's still closer to B than A, what am I doing wrong?

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Making mistakes is a lot better than not doing anything. -Billie Joe Armstrong

otherwiseknownaskyra

Member

Registered: 2014-04-08

Posts: 13

Re: Geometry

Oops, that's not closer to B than A. Apologies, I read it wrong

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Making mistakes is a lot better than not doing anything. -Billie Joe Armstrong

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Geometry

So, you are clear on 18 now?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

otherwiseknownaskyra

Member

Registered: 2014-04-08

Posts: 13

Re: Geometry

Yeah, thanks. I still need help on 7 though, I don't really understand how I'm getting the wrong answer.

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Making mistakes is a lot better than not doing anything. -Billie Joe Armstrong

Bob

Administrator

Registered: 2010-06-20

Posts: 10,164

Re: Geometry

hi otherwiseknownaskyra

Welcome to the forum.

The area of a 9 sided regular polygon is

Divide into 9 isosceles triangles; get area of one; then x by 9.

One triangle = half base x height = half a side x apothem = 3 x side

So whole = 9 x 3 x side

Therefore one side = 117.67 / 27

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Geometry

Hi;

Use this formula for 7.

Now solve for s. Remember to multiply by 9.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

otherwiseknownaskyra

Member

Registered: 2014-04-08

Posts: 13

Re: Geometry

Okay so,

117.67 is the area of the whole thing so 117.67/9=13.074 would be the area of one triangle
13.074/2=6.537
A=bh/2
6.537=6b/2
6.537=3b
2.179=b
And then multiply 2.179(18)=39.222 because 2.179 is just half of the length of one side
So that gives me C!

Thank you guys so much

---

Making mistakes is a lot better than not doing anything. -Billie Joe Armstrong

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Geometry

Congratulations on getting 18 out of 20 by the way.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.