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

    15
    ReputationRep:
    I was doing these exercises, and one question read:
    Without using your calculator, work of the value of cos 270°.

    I got 0. I checked the answers and they said -1. I then used my calculator to double check and it said 0. So what I'm asking is did this textbook make a mistake or am I wrong?
    • Peer Support Volunteers
    • Study Helper
    Offline

    19
    Peer Support Volunteers
    Study Helper
    (Original post by mynameisntbobk)
    I was doing these exercises, and one question read:
    Without using your calculator, work of the value of cos 270°.

    I got 0. I checked the answers and they said -1. I then used my calculator to double check and it said 0. So what I'm asking is did this textbook make a mistake or am I wrong?
    You're right :yy:
    • Thread Starter
    Offline

    15
    ReputationRep:
    (Original post by usycool1)
    You're right :yy:
    Thank you
    • Thread Starter
    Offline

    15
    ReputationRep:
    Also, there's this question that asked:

    Describe geometrically the transformations which map:

    a. The graph of y = tan x° onto the graph of tan (1/2)x°

    I wrote a stretch in the x direction by a factor of 1/2. The answer says a factor of 2

    But then:

    d. The graph of y = sin (x - 10)° onto the graph of sin (x + 10)°.

    I wrote a translation in the x direction by a scale of +20 which was correct.

    How exactly are the answers right when I read them in the same way and order, but got different answers from the answer on one occasion, if that makes sense?
    Offline

    9
    ReputationRep:
    (Original post by mynameisntbobk)
    Also, there's this question that asked:

    Describe geometrically the transformations which map:

    a. The graph of y = tan x° onto the graph of tan (1/2)x°

    I wrote a stretch in the x direction by a factor of 1/2. The answer says a factor of 2

    But then:

    d. The graph of y = sin (x - 10)° onto the graph of sin (x + 10)°.

    I wrote a translation in the x direction by a scale of +20 which was correct.

    How exactly are the answers right when I read them in the same way and order, but got different answers from the answer on one occasion, if that makes sense?
     y = f(kx) is a stretch by scale factor \frac{1}{k}

    y = f(x) -> y = f(x+20) is a translation by -20 in the x direction, so your second answer is wrong.

    I'm fairly sure I'm right, not done graph transformations in a while.
    • Thread Starter
    Offline

    15
    ReputationRep:
    (Original post by Hormonal)
     y = f(kx) is a stretch by scale factor \frac{1}{k}

    y = f(x) -> y = f(x+20) is a translation by -20 in the x direction, so your second answer is wrong.

    I'm fairly sure I'm right, not done graph transformations in a while.
    But I thought that its going from y = sin (x+10)° -> y = sin (x-10)° so the difference is (x-20) and so its a translation of +20 in the x direction.

    Same as I thought its going from y = tan (1/2)x° -> y = tan x°, the factor difference is x2, so the stretch ins the x direction is by a scale factor of 1/2
    Offline

    9
    ReputationRep:
    (Original post by mynameisntbobk)
    But I thought that its going from y = sin (x+10)° -> y = sin (x-10)° so the difference is (x-20) and so its a translation of +20 in the x direction.

    Same as I thought its going from y = tan (1/2)x° -> y = tan x°, the factor difference is x2, so the stretch ins the x direction is by a scale factor of 1/2
    In your question, you said you are going from y = \sin(x-10) to y= \sin(x+10), not what you are saying now.

    y = kx
    \frac{1}{k}y = x

    I think of it like that, when rearrange to make x the subject, the scale factor is what is the coefficient of y.
    • Thread Starter
    Offline

    15
    ReputationRep:
    (Original post by Hormonal)
    In your question, you said you are going from y = \sin(x-10) to y= \sin(x+10), not what you are saying now.

    y = kx
    \frac{1}{k}y = x

    I think of it like that, when rearrange to make x the subject, the scale factor is what is the coefficient of y.
    I think that's what's been confusing me, because the question writes it weird.

    Oh okay, yeah I get that.

    y = (1/2)x
    (1/1/2)y = x
    2y = x, therefore the scale factor is 2.

    Thank you
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: March 10, 2013
Poll
“Yanny” or “Laurel”
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.