Thank you. The only problem is I mentioned that I already know how to solve things like ... ...(Original post by notnek)
I was going to explain how to find but that would involve explaining the exact trig values and using CAST. I don't have time now to do that and don't want to give a short crap explanation.
Instead I'll be lazy and point you to two videos. Together they will show you how to find things like :
https://www.youtube.com/watch?v=MoyVdhHOV_o
https://www.youtube.com/watch?v=VBhAtctYy8g
If I have time tomorrow I can help or maybe someone else will be kind enough to explain.
By the way, I know students who have got an A* in A Level maths without ever learning the exact trig values, since you're allowed a calculator in the exam. But they're a nice tool to be able to attempt certain questions that require them and really understand all the trig concepts.
I want to know how to find the angle for example when... ... without using a calculator

 Follow
 221
 23092016 23:23

 Follow
 222
 23092016 23:26
(Original post by Philipflop)
Thank you. The only problem is I mentioned that I already know how to solve things like ... ...
I want to know how to find the angle for example when... ... without using a calculator
Sketch the two graphs and see where they intersect, look for whichever solution is closest to 0 (the principal solution, in other words)Last edited by RDKGames; 23092016 at 23:28. 
 Follow
 223
 23092016 23:30
(Original post by Philipflop)
Thank you. The only problem is I mentioned that I already know how to solve things like ... ...
I want to know how to find the angle for example when... ... without using a calculator
This is one of the exact values.
So to solve tan x = 1 with CAST, draw in an acute angle of 45 then look for quadrants where tan is negative. 
 Follow
 224
 24092016 01:30
(Original post by RDKGames)
Sketch the two graphs and see where they intersect, look for whichever solution is closest to 0 (the principal solution, in other words)
Would like to know how to use the Trig Ratio triangles for these questions at some point though. Although like notnek said, I'll be allowed a calculator in the exam.
Saying that. Looking at question 1(g) and (h) they look pretty tricky even with a calculator! Not sure how I'm going to rearrange...
EDIT: Actually it was pretty easy to solve using a calculator. But stillLast edited by Philipflop; 24092016 at 01:35. 
 Follow
 225
 24092016 02:13
(Original post by RDKGames)
For you need to know that . You can easily find this from your ratio triangles by considering the 45 degree one, and you know that tan of an angle is opposite side divided by the adjacent one. Since both sides are equal, you get 1/1 which is just 1, but this is something you just remember. Another way to think about it is that tan is the gradient of the hypotenuse. You can see this clearly from the unit circle and the gradient is 1 at 45 degrees. Sine would be the change in y, and cosine would be the change in x, so one over the other gives the gradient.
g and h are pretty easy. You are taking an angle, applying a trigonometric function to it, then applying the inverse of that same trigonometric function. Inverse is like going back a step. So the trig function and its inverse cancel eachother out. It's like dividing by then proceeding to immediately multiply on the same thing. Though for g, it is slightly different, try and see why it is so. Hint: remember that
... but then... ... Is it because of their positioning on the graph?
So for 1(g) I would do this...
Use the trig ratio triangles. The triangle with the angle and use trigonometry's SOH to give me...
arcsin can then be rewritten as...
But then what from here?Last edited by Philipflop; 24092016 at 02:14. 
 Follow
 226
 24092016 02:13
(Original post by Philipflop)
Thank you!! That's a pretty cool way of doing it! Just quite time consuming. But I got there in the end!
Would like to know how to use the Trig Ratio triangles for these questions at some point though. Although like notnek said, I'll be allowed a calculator in the exam.
Saying that. Looking at question 1(g) and (h) they look pretty tricky even with a calculator! Not sure how I'm going to rearrange...
g and h are pretty easy. You are taking an angle, applying a trigonometric function to it, then applying the inverse of that same trigonometric function. Inverse is like going back a step. So the trig function and its inverse cancel eachother out. It's like dividing by then proceeding to immediately multiply on the same thing.
Though for h, it is slightly different. To understand what is going on, you need to think back to when you did inverse graphs. You know that a function can ONLY have an inverse if it is onetoone. The sine function is NOT onetoone therefore we must restrict the domain to and only then we have our inverse. The problem with is that it lies outside our restricted domain. However, thanks to the symmetry of the function, we know that and we can use this to get an angle which is inside our domain while keeping the overall value the same.
Here is a diagram to illustrate this. The black line is and you need to figure out what the purple line is in order to get the correct answer, because the purple one has the same value due to symmetry and how the green dotted line shows it. The orange line represents , the blue dotted line represents while the red line is the blue line with a restricted domain applied to it.
Last edited by RDKGames; 24092016 at 13:55. 
 Follow
 227
 24092016 02:16
(Original post by Philipflop)
Oh right. I'm sort of starting to understand a bit better now. Still a little bit confused as to why things like...
... but then... ... Is it because of their positioning on the graph?
So for 1(g) I would do this...
Use the trig ratio triangles. The triangle with the angle and use trigonometry's SOH to give me...
arcsin can then be rewritten as...
But then what from here?
As far your question is concerned, it goes back to . You can even see it from your ratio triangle with the angle ofLast edited by RDKGames; 24092016 at 02:17. 
 Follow
 228
 24092016 02:18
(Original post by RDKGames)
My post above expands on my previous comment.
As far your question is concerned, it goes back to . You can even see it from your ratio triangle with the angle of 
 Follow
 229
 24092016 02:33
I'm kinda confused with how because of the symmetry
Very good graph btw!! It's helping me visualise the problem so much easier!!Last edited by Philipflop; 24092016 at 02:37. 
 Follow
 230
 24092016 03:02
(Original post by Philipflop)
Just realised we're talking about Q1(h).
Ok. I understand that for sin to be a function it must be onetoone, therefore a restricted domain is put in place. And I can see how the symmetry is used between the black and purple line because doesn't fall within the restricted domain of .
I'm kinda confused with how because of the symmetry
Very good graph btw!! It's helping me visualise the problem so much easier!!
Another way to show it is to use graph transformations:
1. Start with
2. Translate by vector which means
3. Reflect in the yaxis (x=0):
And as you can see, the green graphs is exactly the same as the red one, therefore
Also note, you can use this same transformation technique (with graphs sketches if you wish) to show that andLast edited by RDKGames; 24092016 at 03:10. 
 Follow
 231
 24092016 03:05
(Original post by Philipflop)
Just realised we're talking about Q1(h). Ok. I understand that for sin to be a function it must be onetoone, therefore a restricted domain is put in place. And I can see how the symmetry is used between the black and purple line because doesn't fall within the restricted domain of .
I'm kinda confused with how because of the symmetry
Very good graph btw!! It's helping me visualise the problem so much easier!!Last edited by B_9710; 24092016 at 03:06. 
 Follow
 232
 24092016 13:36
(Original post by RDKGames)
This is about 1g now, you've done h.
Oh dear. Now I'm confused as to where the has come from Likewise, I understand the process of your transformations from the diagrams you showed me, but I'm not sure why it has been transformed in that way? (sorry if that doesn't make sense).
But overall I think I'm beginning to get a grasp on this question. It's almost like sin is cancelled out by the inverse of sin (arcsin). So that...
...the angle from sin can be used to give a ratio using the trig ratio triangle. This gives...
Which is the same as, and can be rewritten...
to which can sort of be written as...
... Where is the angle we are looking for which can be found using the trig ratio triangles.
so...

 Follow
 233
 24092016 13:39
(Original post by Philipflop)
So we're working through Q1(g)...
Oh dear. Now I'm confused as to where the has come from Likewise, I understand the process of your transformations from the diagrams you showed me, but I'm not sure why it has been transformed in that way? (sorry if that doesn't make sense).
But overall I think I'm beginning to get a grasp on this question. It's almost like sin is cancelled out by the inverse of sin (arcsin). So that...
...the angle from sin can be used to give a ratio using the trig ratio triangle. This gives...
Which is the same as, and can be rewritten...
to which can sort of be written as...
... Where is the angle we are looking for which can be found using the trig ratio triangles.
so...
You got 1g correct with a solid method. Hopefully 1h now makes sense as well after the explanations.
The graph has been transformed that way because it has loads of symmetry, so you can do it differently if you wish, but you'd end up with a slightly different form which still gives the right answer.Last edited by RDKGames; 24092016 at 13:42. 
 Follow
 234
 24092016 13:41
(Original post by RDKGames)
Oh sorry, having looked back at the questions, the the is indeed 1h. Not sure what I was thinking saying that at 3am, aha, ignore that part.
You got 1g correct. Hopefully 1h now makes sense as well.
I seriously owe you one!!! 
 Follow
 235
 24092016 13:44
(Original post by Philipflop)
So we're working through Q1(g)...
Oh dear. Now I'm confused as to where the has come from Likewise, I understand the process of your transformations from the diagrams you showed me, but I'm not sure why it has been transformed in that way? (sorry if that doesn't make sense).
But overall I think I'm beginning to get a grasp on this question. It's almost like sin is cancelled out by the inverse of sin (arcsin). So that...
...the angle from sin can be used to give a ratio using the trig ratio triangle. This gives...
Which is the same as, and can be rewritten...
to which can sort of be written as...
... Where is the angle we are looking for which can be found using the trig ratio triangles.
so...
This just comes from the fact that when you compose a function with its inverse . 
 Follow
 236
 24092016 13:48
(Original post by B_9710)
These are standard trig angles. But .
This just comes from the fact that when you compose a function with its inverse .Last edited by Zacken; 24092016 at 13:50. 
 Follow
 237
 24092016 15:03
(Original post by B_9710)
These are standard trig angles. But .
This just comes from the fact that when you compose a function with its inverse . 
 Follow
 238
 24092016 15:37
(Original post by IrrationalRoot)
is not correct. The latter identity is, but the former is not true and is the probably the most misunderstood concept by students when learning trig. is not strictly the inverse of . 
 Follow
 239
 24092016 18:41
(Original post by Philipflop)
^ My head hurts
Hopefully you now see why does not have an inverse. If you're given the value of , you cannot determine . is not onetoone.
Now that begs the question, what is ? I would explain it but it can be quite hard to understand (and will make this post even harder to digest), so it's best to look it up and if you have any questions ask here . The basic idea though is that is the inverse of for a certain portion of the domain of . This portion is chosen so that is onetoone in this portion.
Anyway, it might make you feel better if I told you that none of my teachers understood that does not actually have an inverse lol. They all assumed that , which as I've explained isn't true. 
 Follow
 240
 24092016 18:54
(Original post by IrrationalRoot)
...If so, answer me this question: if , what is ? Is your answer ? Wrong, . In fact could be any even multiple of .Last edited by RDKGames; 24092016 at 20:45.
Write a reply…
Reply
Submit reply
Updated: April 23, 2017
Share this discussion:
Tweet
Related discussions:
TSR Support Team
We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.
This forum is supported by:
 SherlockHolmes
 Notnek
 charco
 Mr M
 TSR Moderator
 Nirgilis
 usycool1
 Changing Skies
 James A
 rayquaza17
 RDKGames
 randdom
 davros
 Gingerbread101
 Kvothe the Arcane
 Airmed
 The Financier
 The Empire Odyssey
 Protostar
 surina16
 nisha.sri
 Reality Check
 claireestelle
 Doonesbury
 furryface12
 Amefish
 harryleavey
 Lemur14
 brainzistheword
 Rexar
 Sonechka
 LeCroissant
 EstelOfTheEyrie
 CoffeeAndPolitics