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# area of sector help

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1. area of sector help
question 9

area of sector=1/2r^2 theta

so area of sector= 1/2r^2 times pie/6 radians

so area of sector= pie/12 times r^2

then i dont know what to do. I need the triangle but in the marked solutions have they done the cosine rule?
2. Re: area of sector help
(Original post by dongonaeatu)
question 9

area of sector=1/2r^2 theta

so area of sector= 1/2r^2 times pie/6 radians

so area of sector= pie/12 times r^2

then i dont know what to do. I need the triangle but in the marked solutions have they done the cosine rule?
First of all, this question is about cake not pie (seriously though - it's pi)

Second: You're doing right so far. That's the area of the whole slice. Now you need to work out the area of the triangle that's cut. Once you have that you know area of triangle must = 1/2 area of sector
3. Re: area of sector help
(Original post by hassi94)
First of all, this question is about cake not pie (seriously though - it's pi)

Second: You're doing right so far. That's the area of the whole slice. Now you need to work out the area of the triangle that's cut. Once you have that you know area of triangle must = 1/2 area of sector
triangle=1/2r^2theta

so i got it as 1/4r^2 but on mark scheme it says its 1/4a^2

oh wait dw is it because the radius is a
4. Re: area of sector help
(Original post by dongonaeatu)
question 9

area of sector=1/2r^2 theta

so area of sector= 1/2r^2 times pie/6 radians

so area of sector= pie/12 times r^2

then i dont know what to do. I need the triangle but in the marked solutions have they done the cosine rule?
The area of triangle can be found using the formula,

So in this question it becomes,

In this question the AREA OF SECTOR = 2 X AREA OF TRIANGLE.
5. Re: area of sector help
(Original post by dongonaeatu)
triangle=1/2r^2theta

so i got it as 1/4r^2 but on mark scheme it says its 1/4a^2

oh wait dw is it because the radius is a

Do a triangle has a radius?

'a' is the length of the sides.
6. Re: area of sector help
(Original post by raheem94)
The area of triangle can be found using the formula,

So in this question it becomes,

In this question the AREA OF SECTOR = 2 X AREA OF TRIANGLE.
area of triangle is also = 1/2r^2sin*theta
7. Re: area of sector help
(Original post by raheem94)

Do a triangle has a radius?

'a' is the length of the sides.
yh thats what i meant soz
8. Re: area of sector help
(Original post by raheem94)

Do a triangle has a radius?

'a' is the length of the sides.
is the picture meant to be just the half of the cake or are we halving the picture
9. Re: area of sector help
(Original post by dongonaeatu)
area of triangle is also = 1/2r^2sin*theta
I think you need to watch this video to first understand the formula.
10. Re: area of sector help
(Original post by dongonaeatu)
area of triangle is also = 1/2r^2sin*theta
Area of sector =

Area of triangle = and since sin(pi/6) = 1/2 then this =

Also, the area of the triangle = 1/2 Area of sector. Solve for a.
11. Re: area of sector help
(Original post by raheem94)
I think you need to watch this video to first understand the formula.
ok, but the area of a triangle is also 1/2r^2sintheta it says it in my book
12. Re: area of sector help
(Original post by hassi94)
Area of sector =

Area of triangle = and since sin(pi/6) = 1/2 then this =

Also, the area of the triangle = 1/2 Area of sector. Solve for a.
ok, but the area of a triangle is also 1/2r^2sintheta it says it in my book

and i got the same answer using that- 1/4a^2
13. Re: area of sector help
(Original post by dongonaeatu)
ok, but the area of a triangle is also 1/2r^2sintheta it says it in my book
Did you watched the video?
14. Re: area of sector help
(Original post by dongonaeatu)
ok, but the area of a triangle is also 1/2r^2sintheta it says it in my book
What is r? That is only true for isosceles triangles if r is the length of two equal sides of a triangle. (i.e. yes it works for this question but that isn't the general area of a triangle formula)
15. Re: area of sector help
(Original post by raheem94)
Did you watched the video?
i am watching the video now
16. Re: area of sector help
(Original post by hassi94)
What is r? That is only true for isosceles triangles if r is the length of two equal sides of a triangle.
i got the right answer 1/4a^2 with the formula

area of a triangle=1/2r^2sintheta
17. Re: area of sector help
(Original post by dongonaeatu)
ok, but the area of a triangle is also 1/2r^2sintheta it says it in my book

and i got the same answer using that- 1/4a^2
It should give , but i was suggesting to watch so that you understand the formula.

The are of sector was,

AREA OF SECTOR = 2 X AREA OF TRIANGLE.

18. Re: area of sector help
(Original post by hassi94)
What is r? That is only true for isosceles triangles if r is the length of two equal sides of a triangle. (i.e. yes it works for this question but that isn't the general area of a triangle formula)
That's why i am suggesting him to watch the video and understand the formula rather than just using it without understanding.
19. Re: area of sector help
(Original post by raheem94)
It should give , but i was suggesting to watch so that you understand the formula.

The are of sector was,

AREA OF SECTOR = 2 X AREA OF TRIANGLE.

yes okay so i could use that formula

area of triangle=1/2absinc

but why do i times it by 2 charlie wants to give half the slice to his m8
20. Re: area of sector help
(Original post by dongonaeatu)
yes okay so i could use that formula

area of triangle=1/2absinc

but why do i times it by 2 charlie wants to give half the slice to his m8
So he wants to give half the slice, which means the complete slice(area of sector) is 2 times the triangle.

Hope it makes sense, just think about it.

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