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C2 - graphs of trigonometric functions. Watch

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    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?
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    (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:
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    (Original post by usycool1)
    You're right :yy:
    Thank you
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    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?
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    (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.
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    (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
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    (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.
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    (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
 
 
 
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