Turn on thread page Beta
    • Thread Starter
    Offline

    7
    ReputationRep:
    Given that angle A is reflex and cosA = root13 / 7
    (a) find the exact value of sinA
    (b) find the exact value of tanA

    I generally understand the question but I need someone to explain the angles and signs to me. If angle A is in quadrant 3 then shouldn't cosA= - root13/7?
    • TSR Support Team
    Offline

    21
    ReputationRep:
    TSR Support Team
    (Original post by Anon736)
    Given that angle A is reflex and cosA = root13 / 7
    (a) find the exact value of sinA
    (b) find the exact value of tanA

    I generally understand the question but I need someone to explain the angles and signs to me. If angle A is in quadrant 3 then shouldn't cosA= - root13/7?
    It'll be in the 4th quadrant surely?
    Offline

    14
    ReputationRep:
    (Original post by Anon736)
    Given that angle A is reflex and cosA = root13 / 7
    (a) find the exact value of sinA
    (b) find the exact value of tanA

    I generally understand the question but I need someone to explain the angles and signs to me. If angle A is in quadrant 3 then shouldn't cosA= - root13/7?
    Reflex angles are greater than 180 degrees, but are also less than 360 degrees so A could be in the fourth quadrant, making it positive.
    • Thread Starter
    Offline

    7
    ReputationRep:
    (Original post by NiamhM1801)
    It'll be in the 4th quadrant surely?
    Well actually thats a good question because a reflex is greater than 180 so I actually don't know if its quadrant 3 or 4.
    Offline

    15
    ReputationRep:
    (Original post by Anon736)
    Given that angle A is reflex and cosA = root13 / 7
    (a) find the exact value of sinA
    (b) find the exact value of tanA

    I generally understand the question but I need someone to explain the angles and signs to me. If angle A is in quadrant 3 then shouldn't cosA= - root13/7?
    Reflex angle covers both 3rd and 4th quadrant since refle angle is angle bigger than π. So this tells you that in fact angle A is in fact in the 4th quadrant. So sinA will be negative and so will tanA - just sketch the graphs and you will see this.
    • Thread Starter
    Offline

    7
    ReputationRep:
    (Original post by h3rmit)
    Reflex angles are greater than 180 degrees, but are also less than 360 degrees so A could be in the fourth quadrant, making it positive.
    For a question like this how do you know which one to use?
    • TSR Support Team
    Offline

    21
    ReputationRep:
    TSR Support Team
    (Original post by Anon736)
    For a question like this how do you know which one to use?
    cosA is positive, therefore it has to be in the 4th. Remember the diagram
    • Thread Starter
    Offline

    7
    ReputationRep:
    (Original post by B_9710)
    Reflex angle covers both 3rd and 4th quadrant since refle angle is angle bigger than π. So this tells you that in fact angle A is in fact in the 4th quadrant. So sinA will be negative and so will tanA - just sketch the graphs and you will see this.
    But why can it not be in the 3rd quadrant?
    • Thread Starter
    Offline

    7
    ReputationRep:
    (Original post by NiamhM1801)
    cosA is positive, therefore it has to be in the 4th. Remember the diagram
    ahhhhhhh
    • Thread Starter
    Offline

    7
    ReputationRep:
    Thanks for the help you guys
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: February 3, 2017
Poll
Favourite type of bread
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

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.