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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. 
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
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