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# Anyone fancy a go at sin x = ? watch

1. I've got this question scanned below for anyone who can help me, i've done parts A and B however part C has got me baffled. The correct answer of AQA website is 0.92. AND THATS THE ONLY ANSWER ALLOWED.

My question is, how the h*ll can they be that exsact when they tell you to read it from a graph, whats the crack have they got glasses with grids on or something because i guess at 0.75 reading from the graph. Surely there's a mathematical way but i don't know it.

2. (Original post by thewebmaster)
I've got this question scanned below for anyone who can help me, i've done parts A and B however part C has got me baffled. The correct answer of AQA website is 0.92. AND THATS THE ONLY ANSWER ALLOWED.

My question is, how the h*ll can they be that exsact when they tell you to read it from a graph, whats the crack have they got glasses with grids on or something because i guess at 0.75 reading from the graph. Surely there's a mathematical way but i don't know it.

(b) 113° (180-67)
(c) 360 - 67 = 293° so this is sin -0.92 using part b
3. it's something i'm working on, also the graph should have been drawn with a pencil however is the graph on the right points. Am i correct in saying that..

sinx.... repeats every 180 STARTS at 00 and goes to 90,1 then 180,0 then 270,-1 then 360,0

cosx... repeats every 180 STARTS at 90,1 and goes (180,0) (270,-1) (360,0)

tanx ="do i need to know this for gcse?"
4. They expect you to use the symmetry of the sin graph I think.
5. hi manps how am i supposed to know that 293 = -0.92. Is this just something they're allowing me to do or is there maths involved. You did 360 - 72 = 293 but how did u get mathemtically from 293 to -0.92.?

i think this is one of those questions i'd lose marks on because its a badly designed question! (when in doubt blaim the question)
6. You've got to notice that 293 is 360-67. sin(360-67) = sin(-67) (because sin repeats every 360°) and since sin is an odd graph, sin(-67) = - sin(67), which is 0.92 as given in the question. That method doesn't use the sketch but to me it's the simplest way.

Using the sketch you could say that going backwards 67° from 360 follows the same pattern as going forwards 67° from 0, only mirrored, so the change in height must be the same as sin67 (and obviously negative since it's all under the axis). You'd still have to notice that 293=360-67 though.
7. (Original post by thewebmaster)
hi manps how am i supposed to know that 293 = -0.92. Is this just something they're allowing me to do or is there maths involved. You did 360 - 72 = 293 but how did u get mathemtically from 293 to -0.92.?

i think this is one of those questions i'd lose marks on because its a badly designed question! (when in doubt blaim the question)
Sin 113 = 0.92
if you add 180° you get sin 293 but the value of this changes to a minus
sorry this is badly explained but you shud be able to see this from the diagram (thats why they ask you to draw it in part a)
8. http://img260.echo.cx/img260/3893/ye...uestion7vm.jpg

there ya go.
9. i've got the idea and i didn't realise that 360 = 293+67
so sort of lost plot and tried to guess/estimate from graph.

10. Don't try to estimate from the graph, it rarely works, especially when they're asking for an answer accurate to a decimal place!

Use the graph to estimate. In this case, you can see 0.92 approx. on the y axis, you can see it occurs twice between 0 and 360 degrees. The first is between 0 and 90 degrees (this is the 67 they give you) and the other is between 90 and 180 degrees. You can see the curve is symmetrical, therefore if the first occurs (90-67=23) 23 degrees to the left of 90, it will also occur 23 degrees to the right of 90, make sense? That makes your answer 90+23, so 113 is your answer!

The second part. It tells you to use your graph, but since when have we read the question? Notice how what they ask is 293? Well, if you look on the graph, the curve around 270 is the same as that around 90, except it's minus! This means if you know the answer for 113 (293-270=23, 90+23=113) then you know the answer for this! 113 was 0.92, and this is the same only minus so the answer is -0.92!

Does this make sense? If not, I'll try and explain a little clearer. I hope this helps.
11. If this is a calculator paper, there's an easier way...
12. (Original post by ljfrugn)
If this is a calculator paper, there's an easier way...
its still easier just to look at the graph.
13. I'm sure typing arcsin 0.92 is quicker than looking for symmetry on a graph. Or maybe not .
14. Yeah, I just wasn't sure if this was a calculator paper or not? If it isn't, I think it's easier to look for symmetry.. If it is, then I agree with you..
15. a) its gcse so they like to keep things simple
b) if you look at the graph of sin(x) and use a bit of common sense taking into fact the graph is symmetric rotationally and at x=90 degrees in the local region etc.. then you are done.
c) if you still reach for your calculator then you will be shot.
16. But I like calculators, I can't do maths without one .
17. (Original post by ljfrugn)
But I like calculators, I can't do maths without one .
u dont use calculators at uni, if ur planning on studying maths at uni then you should lose some of that dependce on calculators
18. Probably, I use them more to check my answers than anything else, it's nice in an exam to know you've got something right before moving on to the next question. Not looking forward to the AEA, no calculators, so you never really know when you're expected to work something out and when to just leave it as a power of something etc.
19. firstly whats with the comical handwriting and graph drawing. and secondly isnt that just a little bit obvious (even i can do it and im [predicted a C)
20. (Original post by thinktank)
firstly whats with the comical handwriting and graph drawing. and secondly isnt that just a little bit obvious (even i can do it and im [predicted a C)
FFS, grow up. If you can't say anything useful, don't say anything at all .

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