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

    14
    My question is, how is one of the solutions 231?
    Okay...I figured out how. I don't understand why. You add 180 to 131 and - 80 to get 231.
    Name:  image.jpg
Views: 96
Size:  500.5 KB

    I followed the method in my book, I haven't a clue what's going one to be frank.

    (I'm aware that 411 is wrong as its not in the 0-360 range)
    Why would you add 180? And Not 360?

    I know I sound really stupid, but I'm stuck. Will someone mind explaining this to me? And yes, I do realise this is supposed to be simple. *sigh*
    • Community Assistant
    • Study Helper
    Offline

    20
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by Questioness)
    My question is, how on this bloody earth is one of the solutions 231?
    Okay...I figured out how. I don't understand why. You add 180 to 131 and - 80 to get 231.
    Name:  image.jpg
Views: 96
Size:  500.5 KB

    I followed the method in my book, I haven't a clue what's going one to be frank.

    (I'm aware that 411 is wrong as its not in the 0-360 range)
    Why would you add 180? And Not 360?

    I know I sound really stupid, but I'm stuck. Will someone mind explaining this to me? And yes, I do realise this is supposed to be simple. *sigh*
    Your mistake is where you've done 180 - 49 = 131.

    You may be confusing this with sine : sin(x) = sin(180-x) but that's not true for cos.

    If you check \cos(131) on your calculator you'll see it's not equal to 0.66.

    Are you able to correct your working? If you're still stuck, can you tell us which method you have been taught to find multiple trig solutions? E.g. CAST, using the graphs etc.
    • Thread Starter
    Offline

    14
    (Original post by notnek)
    Your mistake is where you've done 180 - 49 = 131.

    You may be confusing this with sine : sin(x) = sin(180-x) but that's not true for cos.

    If you check \cos(131) on your calculator you'll see it's not equal to 0.66.

    Are you able to correct your working? If you're still stuck, can you tell us which method you have been taught to find multiple trig solutions? E.g. CAST, using the graphs etc.
    Ahh, right. I was following the method in the textbook. It uses sin as an example. Do you take 49 away from 360, to get 311? Cos(311) =0.66

    I'm following this method:
    Name:  image.jpg
Views: 36
Size:  506.3 KB
    Offline

    2
    ReputationRep:
    For cos you can just 360- first solution instead of 180 like you do for sin
    • Thread Starter
    Offline

    14
    Why do you not add 360 to 311.
    It's just 311-80=231
    Whereas a for 49, it's 49+360= 409-80 =329. Name:  image.jpg
Views: 42
Size:  502.3 KB
    • Community Assistant
    • Study Helper
    Offline

    20
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by Questioness)
    Why do you not add 360 to 311.
    It's just 311-80=231
    Whereas a for 49, it's 49+360= 409-80 =329. Name:  image.jpg
Views: 42
Size:  502.3 KB
    \theta + 80 = 49

    \theta + 80 = 360 - 49 = 311

    \theta + 80 = 49 + 360 = 409

    \theta + 80 = 311 + 360 = 671

    Does any of this not make sense?

    You can solve each of the above equations and see which ones give you solutions in the range 0\leq \theta\leq 360.
    • Thread Starter
    Offline

    14
    (Original post by notnek)
    \theta + 80 = 49

    \theta + 80 = 360 - 49 = 311

    \theta + 80 = 49 + 360 = 409

    \theta + 80 = 311 + 360 = 671

    Does any of this not make sense?

    You can solve each of the above equations and see which ones give you solutions in the range 0\leq \theta\leq 360.
    Makes perfect sense. Thanks.
 
 
 
Poll
Do you agree with the PM's proposal to cut tuition fees for some courses?
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.