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Topic review (newest first)

bob bundy
2012-11-07 08:54:21

hi zee-f

Oh, well done.  I'm so pleased.  Both correct in my opinion.  smile

Bob

zee-f
2012-11-07 07:09:01

Hi Bob,


15. r=y n=x

#15- My new answer is (E) x*y*pi/180

I pretended that x was 1 and said that
(1/360 * 2= 1/180) then put the x back and multiplied. I get x*y*pi/180.

#10- OK sense I know that c=π*d and D= c/π
I am going to divide the circumference by PI So I will get(x+y)π/π , and
π/π = 1 so I am left with (x+y) and to get the radius I am going to divide by two and my answer is (x+y)/2.

Thank you,

bob bundy
2012-11-05 09:47:37

hi zee-f

Very well done for getting 18/20 at first attempt.  That's really good!

I can see where you went wrong here with Q15, so I'll do it first.

I choose A it was incorrect I am still working on the correction

What is the length of the arc if

15. r=y n=x
A  x*y*pi/90
B x*y*pi/30
C x*y*pi/45
D x*y*pi/27
E  x*y*pi/180
F  x*y*pi/115

With these problems I first work out the whole circumference, and then work out the fraction for the arc.





So cancel a 2 top and bottom and it's done.

Now for question 10.

What is the circumference of the circle if the radius is:

10. (x + y)pi

A (x+y)/7
B (x+y)/5
C(x+y)/1
D(x+y)/2
E (x+y)/3
F (x+y)/8

So I know the the formula for the circumference of a circle is 2(pi)(r)

So it would be 2(pi)*((x + y)pi) right? but then what do I do ?

What you have done is exactly right so something else is wrong here.

If the radius has a pi in it,   the circumference will collect another,  giving a pi squared.  None of the answers looks right.

If it's a mis-print I can make sense of it.  Try this:

What is the radius of the circle if the circumference is:

10. (x + y)pi

A (x+y)/7
B (x+y)/5
C(x+y)/1
D(x+y)/2
E (x+y)/3
F (x+y)/8

This way round it makes sense and one of the answers works.

Bob

zee-f
2012-11-05 08:16:59

I started the next lesson about Circumference and Arc Length and I got all the 18/20
I am stuck on the 2 questions I got incorrect :

I choose C it was incorrect

What is the circumference of the circle if the radius is:

10. (x + y)pi

A (x+y)/7
B (x+y)/5
C(x+y)/1
D(x+y)/2
E (x+y)/3
F (x+y)/8

So I know the the formula for the circumference of a circle is 2(pi)(r)

So it would be 2(pi)*((x + y)pi) right? but then what do I do ?


I choose A it was incorrect I am still working on the correction
What is the length of the arc if
15. r=y n=x
A  x*y*pi/90
B x*y*pi/30
C x*y*pi/45
D x*y*pi/27
E  x*y*pi/180
F  x*y*pi/115


L =
(n/360)(2(PI)r) where L = length, n = degree measure of arc, and r = radius of the circle.

zee-f
2012-11-05 07:48:51

No I did #20 and got it correct smile

I choose D

20. If line segment BC has a length of 24, and line segment AB has a length of 18, what is the radius of the circle?
A 18
B 38
C 6
D 15
E 4
F 29

bob bundy
2012-11-05 06:23:13

You are very welcome.

By my reckoning only Q20 to go or have you done that?

Bob

zee-f
2012-11-05 06:21:38

Thank you for the help!

bob bundy
2012-11-05 05:57:46

Yes, that's it.  Excellent!

Bob

bob bundy
2012-11-05 05:56:35

The thing is this.  There is a property that is always true for all circles and Q19 is testing it.

Amongst all your answers, you have said it correctly, but I don't want you to get it by luck, I want you to be sure.

So, looking at my multi-coloured diagram, what is angle D every time?

Bob

zee-f
2012-11-05 05:54:59

is always a right angle right?

zee-f
2012-11-05 05:49:29

I said #102 before seeing post #101

zee-f
2012-11-05 05:48:13

when I measure the one you drew on the screen I get A is 30 degrees C is 70 D is 80

bob bundy
2012-11-05 05:45:21

You've made up 60 and 30 because that's what those angles look like.  But remember D could be anywhere on the circumference.

I've added a few more possibilities in different colours.

But in a way you're right because the angle at D is always ...... ?

Bob

zee-f
2012-11-05 05:43:31

I drew a circle and the first half is 30, 30, 120 the second is 60 60 60 it looks exactly like your triangle in the diagram but cut in half at 120

zee-f
2012-11-05 05:40:35

but i think i should add 60 +30 which gives me 90

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