Hey there! Sign in to join this conversationNew here? Join for free
Turn on thread page Beta
    • Thread Starter
    Offline

    15
    ReputationRep:
    Can I assume <ABC is 45 degrees since AB is a straight line and AB is a straight line? I think that only applies to circle thereom.

    Also, work out the area of the original square piece of card.

    Posted from TSR Mobile
    Attached Images
     
    Offline

    21
    ReputationRep:
    (Original post by Moltenmo)
    Can I assume <ABC is 45 degrees since AB is a straight line and AB is a straight line? I think that only applies to circle thereom.

    Also, work out the area of the original square piece of card.

    Posted from TSR Mobile
    Yes.
    it is the exterior angle of a regular octagon and the sum of exterior angles of a polygon is 360
    Also you know AC and BC are the same length so it's an isosceles triangle and therefore the two base angles are equal


    Posted from TSR Mobile
    • Thread Starter
    Offline

    15
    ReputationRep:
    (Original post by gdunne42)
    Yes.
    it is the exterior angle of a regular octagon and the sum of exterior angles of a polygon is 360
    Also you know AC and BC are the same length so it's an isosceles triangle and therefore the two base angles are equal


    Posted from TSR Mobile
    Damn, I didn't even think about exterior angles for some stupid reason. Thank you.

    Posted from TSR Mobile
    Offline

    1
    ReputationRep:
    1. Calculate the area of the octagon using sine rule.

    2. Calculate the area of the little right-angled triangle.
    1) Calculate the length AB using cosine rule.

    2) Calculate the length CB, given that angle ABC is 45 degrees.

    3) Given that AC=CB and the triangle is right-angled. Find the area.

    Add the area of the octagon and the triangles to get the total area.
    Good luck!
    Offline

    19
    ReputationRep:
    (Original post by Delia_*)
    The area of of original square should be approximately ...
    Please don't post dull slutions - it's against the rules of the Maths forum.
    Offline

    1
    ReputationRep:
    (Original post by Muttley79)
    Please don't post dull slutions - it's against the rules of the Maths forum.
    sorry, I never knew that there's such a rule. All I wanted was to help. Sorry again
    Offline

    15
    ReputationRep:
    There's different ways to work out the area of the square, but I personally would have used cosine rule to work out AB, then used pythagoras to work out AC and CB (because they'd be the same), and then added AB to 2AC and squared that. But that's just my way, other ways would work too.

    I think that would work, sorry if it doesn't, someone please correct me!
    • Thread Starter
    Offline

    15
    ReputationRep:
    (Original post by IfYouCanDreamIt)
    There's different ways to work out the area of the square, but I personally would have used cosine rule to work out AB, then used pythagoras to work out AC and CB (because they'd be the same), and then added AB to 2AC and squared that. But that's just my way, other ways would work too.

    I think that would work, sorry if it doesn't, someone please correct me!
    How do you assume AC and CB are the same? It doesn't say or show that in the question?

    Posted from TSR Mobile
    Offline

    21
    ReputationRep:
    (Original post by Moltenmo)
    How do you assume AC and CB are the same? It doesn't say or show that in the question?

    Posted from TSR Mobile
    Because of how you made them. You have removed a regular octagon from a square.
    And also because of the exterior angle business, both angles in each triangle are 45 degrees so you must have an isosceles triangle.

    Posted from TSR Mobile
    Offline

    15
    ReputationRep:
    (Original post by Moltenmo)
    How do you assume AC and CB are the same? It doesn't say or show that in the question?

    Posted from TSR Mobile
    (Original post by gdunne42)
    Because of how you made them. You have removed a regular octagon from a square.
    And also because of the exterior angle business, both angles in each triangle are 45 degrees so you must have an isosceles triangle.

    Posted from TSR Mobile
    Yeah you summed it up well, I wasn't sure how to explain it. It might not explicitly say that they are the same but I think you'd be expected to be able to figure that out yourself if a question like this came up on an exam.
 
 
 
Poll
“Yanny” or “Laurel”
Useful resources

Study tools

Rosette

Essay expert

Learn to write like a pro with our ultimate essay guide.

Thinking about uni already?

Thinking about uni already?

See where you can apply with our uni match tool

Student chat

Ask a question

Chat to other GCSE students and get your study questions answered.

Creating

Make study resources

Create all the resources you need to get the grades.

Planner

Create your own Study Plan

Organise all your homework and exams so you never miss another deadline.

Resources by subject

From flashcards to mind maps; there's everything you need for all of your GCSE subjects.

Papers

Find past papers

100s of GCSE past papers for all your subjects at your fingertips.

Help out other students

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

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

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