The Student Room Group
<a https://www.thestudentroom.co.uk/showthread.php?t=7467335'> Year 12s: what will be the first way you research your future options? >>
<a https://www.thestudentroom.co.uk/showthread.php?t=7467335'> Year 12s: what will be the first way you research your future options? >>
<a https://www.thestudentroom.co.uk/showthread.php?t=7467335'> Year 12s: what will be the first way you research your future options? >>

Trig equation/stationary value

"here are two statements about a stationary value for the function f(x)=4sinx-2;


1) f has a stationary value when x= (π/3)

2) f has a stationary value when x=(π/2)

I simplified the equation so that it was equal to 1/2 (one half).

I then looked at the exact value of sin 1/2; which is equal to 30 degrees.

I thought that meant that neither statement was correct; because 1) is equal to 60 degrees; and 2) is equal to 90 degrees.

However, the answers specify that 2) is correct.
Original post by apronedsamurai
...


f(x)=0 f(x) = 0 does not solve to give stationary points.
Original post by apronedsamurai

I simplified the equation so that it was equal to 1/2 (one half).

I then looked at the exact value of sin 1/2; which is equal to 30 degrees.



These 2 statements make no sense at all

What would you normally do to find the stationary points of a curve?
If this is A2, you need to differentiate the function and find where the differential is equal to 0.

If this is AS, don't worry, look and the sine graph and find the points where the graph is parallel to the x axis
Reply 4
Avatar for User947387
User947387
OP
17
No graph is provided.
differentiate you must
Reply 6
Avatar for User947387
User947387
OP
17
I thought 4sinx-2=0
4sinx=2
sinx=2/4 simplified to 1/2

sin 1/2 (30 degrees)

Err, differentiate? I thought that might be the case, but that I had no idea how to do that....4sin?

Or would it differentiate to simply sin; meaning that the normal sin function is used, where 4 would be the maximum point; and so it would pass through the 90 degree mark?
(edited 9 years ago)
Original post by apronedsamurai
No graph is provided.

Draw a graph if one isn't provided. If this is AS, you don't need to differentiate it.
Original post by apronedsamurai
I thought 4sinx-2=0
4sinx=2
sinx=2/4 simplified to 1/2

sin 1/2 (30 degrees)

Err, differentiate? I thought that might be the case, but that I had no idea how to do that....4sin?


Are you doing AS or A2?

Do you know what the graph of Sin(x) looks like?
Reply 9
Avatar for User947387
User947387
OP
17
Im in Scotland, so dont know what AS and AS2 are.

This is "Higher"

Yes, I know what the (original, i.e. unmodified) graph of Sin(x) looks like.

Maximum value of 1; Min. value of -1; intersects at 90 and 180 degrees respectively.
(edited 9 years ago)
Original post by apronedsamurai
Im in Scotland, so dont know what AS and AS2 are.

This is "Higher"


Do you know about differentiation
Can you differentiate Sin(x)

If Not

Do you know what the graph of Sin(x) looks like?
Do you know what a stationary point is?
Original post by apronedsamurai
Im in Scotland, so dont know what AS and AS2 are.

This is "Higher"

Basically if you now how to differentiate sinx, you have to differentiate. If you don't, you have to use the graph.
Original post by apronedsamurai
Im in Scotland, so dont know what AS and AS2 are.

This is "Higher"

Yes, I know what the (original, i.e. unmodified) graph of Sin(x) looks like.

Maximum value of 1; Min. value of -1; intersects at 90 and 180 degrees respectively.


draw the sin graph, where does the gradient = 0? (that is definition of stationary point)
So sketch a graph of the translated sin(x) graph and use it to find the maximum and minimum points.
Reply 14
Avatar for davros
davros
16
Original post by apronedsamurai
Im in Scotland, so dont know what AS and AS2 are.

This is "Higher"

Yes, I know what the (original, i.e. unmodified) graph of Sin(x) looks like.

Maximum value of 1; Min. value of -1; intersects at 90 and 180 degrees respectively.


What definition does your textbook use for "stationary point"? You're almost certainly expected to use differentiation for this!
Original post by davros
What definition does your textbook use for "stationary point"? You're almost certainly expected to use differentiation for this!

I don't think they know how to differentiate trig functions. Either they haven't covered it yet and they are trying to do questions that they haven't covered the methods for, or the question has to be solved graphically.
Reply 16
Avatar for davros
davros
16
Original post by morgan8002
I don't think they know how to differentiate trig functions. Either they haven't covered it yet and they are trying to do questions that they haven't covered the methods for, or the question has to be solved graphically.


That's what I'm trying to get the OP to communicate.

There's no point in introducing the concept of "stationary point" prior to covering differentiation, because there isn't going to be a systematic way of tackling questions like this without that (obviously you "get lucky" with trig functions because the derivative of sin is just cos, which you know how to inspect!).
Can this thread be closed please? Im getting a bit uncomfortable with it.
Original post by davros
That's what I'm trying to get the OP to communicate.

There's no point in introducing the concept of "stationary point" prior to covering differentiation, because there isn't going to be a systematic way of tackling questions like this without that (obviously you "get lucky" with trig functions because the derivative of sin is just cos, which you know how to inspect!).

Well at A-level you cover polynomial differentiation in C1, but don't cover trig differentiation until C3, so it's possible to know what a stationary point is without being able to solve the question via differentiation.
Original post by apronedsamurai
Can this thread be closed please? Im getting a bit uncomfortable with it.


:confused::confused:

If you just tell us what your knowledge of stationary points is we can help

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you