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Don't understand this ?

H.
(edited 7 years ago)
Reply 1
Avatar for sdvds
sdvds
2
cos-1

sin-1

get values for cos as + or - 360

get values for sin + 180
For cos(x)=0.5, go up to where 0.5 is on the y-axis and then move along until you 'hit' the y=cosx graph. Then go down to the x-axis and this tells you the value.

There is more than one value though so you need to go along and down more than once. :smile:

Original post by sdvds
cos-1

sin-1

get values for cos as + or - 360

get values for sin + 180

No it says to use the graph.
Reply 3
Avatar for TeeEm
TeeEm
19
Original post by sdvds
cos-1

sin-1

get values for cos as + or - 360

get values for sin + 180


draw horizontal lines at y =0.5 and y = 0.25 and look for intersections

EDIT
too many of us here...
I am out!
(edited 9 years ago)
Original post by iamspiderman
How would I go about working this out? It looks very complicated..



You should use your calculator to find the first answer

Then look at the relevant graph ... You should be able to see repetition and symmetry in the graph ... This will give you other values of x that have the same sine or cosine
..
(edited 7 years ago)
Original post by iamspiderman
Ok well I've tried and got :

Cos^-1 (0.5) =60 degrees
(This is the first angle on x axis)

Cos x = +0.5 for all of the following angles:
60, 110, 150,210,240,300,330,390

I can see symmetry as 60 degrees is 30 degrees away from the peak (90 degrees )


That is the correct understanding of the symmetry



Consider your 150 answer ... Look at x is 150 on the graph ... Does the graph go through (150, 0.5)


Draw a line across at 0.5 look at where this crosses the cos graph ... You should only see 3 possible values
(edited 9 years ago)
[.
(edited 7 years ago)
Original post by iamspiderman
Ok so 110 is wrong and should be 120?

So the values are:
60,120,330 and 390 ?


Why do you think that 120 is correct .... Look at the graph
..
(edited 7 years ago)
Original post by iamspiderman
Yeah it is wrong I've been looking at it incorrectly
I think the values are 60, 300 and I'm not sure about the third one


Can you explain why you think 300 is a solution
..
(edited 7 years ago)
Original post by iamspiderman
I have just been taking 30 degrees away from each peak or adding 30 degrees


Have you actually been looking at the graph ... You need places that equal 0.5
..
(edited 7 years ago)
Reply 14
Avatar for davros
davros
16
Original post by iamspiderman
By looking at the graph the second point is around 315 but when I do cos(315) it doesn't equal 0.15
Like cos(60) equals 0.15
But for the second point 279 equals 0.15


Where've you got 0.15 from - you should be looking for values that give 0.5! Or was that just a typo?
Original post by iamspiderman
By looking at the graph the second point is around 315 but when I do cos(315) it doesn't equal 0.15
Like cos(60) equals 0.15
But for the second point 279 equals 0.15


You have lost me

You know from symmetry that 315 is not right, nor is 379

Where has this 0.15 come from
..
(edited 7 years ago)

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