Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    2
    ReputationRep:
    Name:  question.PNG
Views: 115
Size:  37.6 KB
    Part a answer=120cm^2
    With part b in the question which is on the attachment, why can't you do
    A=1/2 absinC
    120=(17)(17)sinC=120
    C=0.98 radians

    So angle COD= 0.98 radians
    Why is this wrong? The correct answer=2.16 radians

    Thank you.
    Offline

    16
    ReputationRep:
    (Original post by krisshP)
    Name:  question.PNG
Views: 115
Size:  37.6 KB
    Part a answer=120cm^2
    With part b in the question which is on the attachment, why can't you do
    A=1/2 absinC
    120=(17)(17)sinC=120
    C=0.98 radians

    So angle COD= 0.98 radians
    Why is this wrong? The correct answer=2.16 radians

    Thank you.
    Ignore me I am dim !!!!!!!!!
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by TenOfThem)
    Because 1/2 ab SinC works in degrees
    THANKS
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by TenOfThem)
    Because 1/2 ab SinC works in degrees
    Can you please help me with part c:
    Calculate, giving answers to 2 decimal places:
    The area of the shaded region R.

    Here's my working out:
    Area of shaded region R=total area of larger sector with arc A1 - area of smaller sector with arc A2

    Area of shaded region R=CA1D total area - CA2D area
    =\frac{1}{2}(15)^2 (\pi) - \frac{1}{2}(17)^2 (\pi)

=-32\pi

    This wrong, but why? How do you do this question.
    Offline

    16
    ReputationRep:
    (Original post by krisshP)
    Can you please help me with part c:
    Calculate, giving answers to 2 decimal places:
    The area of the shaded region R.

    Here's my working out:
    Area of shaded region R=total area of larger sector with arc A1 - area of smaller sector with arc A2

    Area of shaded region R=CA1D total area - CA2D area
    =\frac{1}{2}(15)^2 (\pi) - \frac{1}{2}(17)^2 (\pi)

=-32\pi

    This wrong, but why? How do you do this question.

    Well it is wrong because it is nonsense

    The \frac{1}{2} \pi 15^2 is good as that is the semicircle centre M

    But then you need to take away the segment (which is the sector minus the triangle)
    Offline

    9
    ReputationRep:
    (Original post by krisshP)
    Name:  question.PNG
Views: 115
Size:  37.6 KB
    Part a answer=120cm^2
    With part b in the question which is on the attachment, why can't you do
    A=1/2 absinC
    120=(17)(17)sinC=120
    C=0.98 radians

    So angle COD= 0.98 radians
    Why is this wrong? The correct answer=2.16 radians

    Thank you.
    The equation 1/2 ab sin C for the area of a triangle works just as well in radians as it does in degrees. The problem you have is that, having correctly established that the sine of the angle you are interested in is 240/289, you have trusted your calculator to tell you what the angle is. And it has told you one possible value - but it is not the value you want! Can you see why not, and which of the other values (out of an infinite number of possibilities) is the one that you really want?
    Offline

    16
    ReputationRep:
    (Original post by Pangol)
    The equation 1/2 ab sin C for the area of a triangle works just as well in radians as it does in degrees.
    Me being thick !
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by Pangol)
    The equation 1/2 ab sin C for the area of a triangle works just as well in radians as it does in degrees. The problem you have is that, having correctly established that the sine of the angle you are interested in is 240/289, you have trusted your calculator to tell you what the angle is. And it has told you one possible value - but it is not the value you want! Can you see why not, and which of the other values (out of an infinite number of possibilities) is the one that you really want?
    pi - 0.98=2.16 This is supposed to be the correct answer, not 0.98. I understand why since there are 2 solutions from the sine curve where you get the same value.

    THANKS
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Would you like to hibernate through the winter months?
    Useful resources

    Make your revision easier

    Maths

    Maths Forum posting guidelines

    Not sure where to post? Read the updated guidelines here

    Equations

    How to use LaTex

    Writing equations the easy way

    Student revising

    Study habits of A* students

    Top tips from students who have already aced their exams

    Study Planner

    Create your own Study Planner

    Never miss a deadline again

    Polling station sign

    Thinking about a maths degree?

    Chat with other maths applicants

    Can you help? Study help unanswered threads

    Groups associated with this forum:

    View associated groups
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.