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# C2 - graphs of trigonometric functions. watch

1. 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?
2. (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
3. (Original post by usycool1)
You're right
Thank you
4. 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?
5. (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?
is a stretch by scale factor

-> 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.
6. (Original post by Hormonal)
is a stretch by scale factor

-> 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
7. (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 to , not what you are saying now.

I think of it like that, when rearrange to make x the subject, the scale factor is what is the coefficient of y.
8. (Original post by Hormonal)
In your question, you said you are going from to , not what you are saying now.

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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