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# C2 Trig help watch

1. Question 7 a and b if possible.
https://c4a3f001dcd45afe69d0ceec8300...%20Edexcel.pdf

I can never understand how to do these type of qestions. I would be very grateful if someone could give me a bit of guidance on it. Much appreciated.
Thanks!
2. For the first one: sin(theta+60)=4/9; sin^-1(4/9) = theta+60

you want to make the range (0 +60) </= (theta+60) < (360 + 60)

then take 60deg away from your results.

For the second: if you times by cosx you get 2sinx - 3 sinxcosx = 0;
Put in another form, sinx(2-3cosx)=0; Therefore sinx = 0 or cosx=2/3
3. For part b if you factorise to give
then it should become a lot more clear.
or .

What you should not do in this situation is divide by sinx as you will lose answers. You should try and factorise as I have done.
4. Looks like i was beaten to it but i did this paper earlier and got full marks on this question so here is how i got part b. Feel free to ask any further questions if you have any :3
5. Cosx=3/2 sinx=0 find both answers in radians to get values and then make them negative to get two more values. The answers would the ones in the range.
6. (Original post by Thomith)
Looks like i was beaten to it but i did this paper earlier and got full marks on this question so here is how i got part b. Feel free to ask any further questions if you have any :3
Could you possibly do it for part a as well please.
7. Heres what i got, but i didnt show much of my working out. Basically you Sin-1 both sides (assuming you only have a "1sin" notice how i divided by 9 first). Then change the limits depending on what accompanies the "Theta". Then because the answer is positive, only use parts of CAST where Sin is positive (A and S) and then -60 both sides and only put down answers between the original limits.
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8. (Original post by Thomith)
Heres what i got, but i didnt show much of my working out. Basically you Sin-1 both sides (assuming you only have a "1sin" notice how i divided by 9 first). Then change the limits depending on what accompanies the "Theta". Then because the answer is positive, only use parts of CAST where Sin is positive (A and S) and then -60 both sides and only put down answers between the original limits.
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Could you explain how you got those values of theta+60 and then the two values for theta at the end please.
9. (Original post by Atiq629)
Could you explain how you got those values of theta+60 and then the two values for theta at the end please.
http://www.examsolutions.net/a-level...5&solution=7.1

Watch that. (Personally I prefer to draw out the sin graph)

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