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# Help with this maths question watch

1. Hello,

Can you help me with question 4 of this A Level exam? It's Pure Maths 1 from CIE which I think is roughly equivalent to C1 or C2.

I've seen the mark scheme but I still don't understand how they got to that answer.

Any help would be greatly appreciated.

Thank you.
2. (Original post by t.s.r.)
Hello,

Can you help me with question 4 of this A Level exam? It's Pure Maths 1 from CIE which I think is roughly equivalent to C1 or C2.

I've seen the mark scheme but I still don't understand how they got to that answer.

Any help would be greatly appreciated.

Thank you.
area of sector = 1/2 * r^2 * theta

using 1/2 * absin(C):
area of triangle = 1/2 * r^2 * sin(theta)

area of triangle = area of segment
Therefore: 1/2 * r^2 * theta - 1/2 * r^2 * sin(theta) = 1/2 * r^2 * sin(theta)

Rearrange from here to get 2sin(theta) = theta
3. (Original post by SherlockHolmes)
area of sector = 1/2 * r^2 * theta

using 1/2 * absin(C):
area of triangle = 1/2 * r^2 * sin(theta)

area of triangle = area of segment
Therefore: 1/2 * r^2 * theta - 1/2 * r^2 * sin(theta) = 1/2 * r^2 * sin(theta)

Rearrange from here to get 2sin(theta) = theta
Oh, okay! Got it!

I wasn't able to do it straightaway because the formula for the area of a triange using the sine of an angle is not in the syllabus so it didn't cross my mind at all to use that one. I was using the common formula height*base/2.

Anyway, thanks a lot!

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Updated: January 25, 2015
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