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Area of a Sector

  • 29-01-2011 3:31pm
    #1
    mulciber
    Registered Users, Registered Users 2 Posts: 200 ✭✭


    Hi, I'm in Transiton year and I'm doing higher level maths but I'm having trouble with this question:

    I have to find the area of the sector.
    Radian= 0.7
    1/2 diameter= 10cm

    This is the way I've been doing it:

    (1/2)(r squared)(theta)
    (1/2)(0.7 squared)(10cm)
    Answer= 2.45cm squared.

    I don't feel that this is the right answer. I don't know why though. :confused:
    If I'm doing this wrong/right could you please tell me.
    Any help would be appreciated.

    Thanks. :D


Comments

  • #2
    LeixlipRed
    Closed Accounts Posts: 6,081 ✭✭✭LeixlipRed


    You've got a lot of things confused here. The formula for the area of a sector is 1/2*radius^2*theta. Where theta is the angle is radian measure. The radius is half the diameter of the circle. You seem to have mixed radians and radius up.


  • #3
    sponsoredwalk
    Registered Users, Registered Users 2 Posts: 3,038 ✭✭✭sponsoredwalk


    You have to find the area in a sector of a circle that is 0.7 radians in area?

    The area of a circle is A = πr² where π is the constant "pi" = 3.14159...

    1: Do you know what the diameter is?

    2: Do you know what half the diameter is?

    3: Do you know what a radian is?

    4: How does a radian relate to the whole circle?

    If you don't know the answers to any of these do a bit of study on the net
    to find out & let us know, all I'll say is that theta = 10cm makes no sense ;)


  • #4
    mulciber
    Registered Users, Registered Users 2 Posts: 200 ✭✭mulciber


    LeixlipRed wrote: »
    You've got a lot of things confused here. The formula for the area of a sector is 1/2*radius^2*theta. Where theta is the angle is radian measure. The radius is half the diameter of the circle. You seem to have mixed radians and radius up.

    Ohhhh, so r= raidus and theta= radians? Ok, I get it now. Thanks a million. :D


  • #5
    mulciber
    Registered Users, Registered Users 2 Posts: 200 ✭✭mulciber


    sponsoredwalk wrote: »
    You have to find the area in a sector of a circle that is 0.7 radians in area?

    The area of a circle is A = πr² where π is the constant "pi" = 3.14159...

    1: Do you know what the diameter is?

    2: Do you know what half the diameter is?

    3: Do you know what a radian is?

    4: How does a radian relate to the whole circle?

    If you don't know the answers to any of these do a bit of study on the net
    to find out & let us know, all I'll say is that theta = 10cm makes no sense ;)

    Yeah, I know 1 and 2. they're easy.

    3: A radian is an alternative measurement to degrees. Eg. 2pie radians= 360 degrees.

    4: 2pie raidans is a circle. I was just trying to find the sector but I got mixed up between the raidus and radians. I thought theta represented the radius (1/2 the diameter) but it actually represents the radians and r represents the radius. So i get how to do it now. Thanks. :)


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