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# C2 Trig Help! watch

1. a) Find all possible values of sin C for which cos C = 1/2.
b) Find the values of D for which -180 degrees <D< 180 degrees and tan D = 5 sin D.

Right so for part a), I did cos-1 (1/2) = 60, and then sin 60 = root 3 / 2. I am told that this is one of the answers, and the other is meant to be - root 3 / 2, how do I get this?

I don't know how to approach part b), so any help on both would be really appreciated thanks!
2. for c2 you only learn 2 things:

cos^2 x + sin^2 x =1

tanx=(sinx)/(cosx)

sin is postive for angles between 0 and 180 and negative 180< to 360, cos is positive for angles 0 to 90 and 270 to 360 negative 90-270

use these in a) and b) in a way you think helps you the most.......
3. you get by looking at your graph of and figuring out that there is another value C for which
I'm assuming somewhere in the question it says

for b, I'd try to find a value D for which both sind and tand = 0. because then 5sind and tand will = 0.
4. (Original post by mathz)
for c2 you only learn 2 things:

cos^2 x + sin^2 x =1

tanx=(sinx)/(cosx)

sin is postive for angles between 0 and 180 and negative 180< to 360, cos is positive for angles 0 to 90 and 270 to 360 negative 90-270

use these in a) and b) in a way you think helps you the most.......
So for a), to get the other answer you would do 360 - 60 = 300, and then do sin 300 = - root 3/2?
a) Find all possible values of sin C for which cos C = 1/2.
b) Find the values of D for which -180 degrees <D< 180 degrees and tan D = 5 sin D.

Right so for part a), I did cos-1 (1/2) = 60, and then sin 60 = root 3 / 2. I am told that this is one of the answers, and the other is meant to be - root 3 / 2, how do I get this?

I don't know how to approach part b), so any help on both would be really appreciated thanks!
awwwwwwwww, its been about 7 months since i didnt do any maths, i miss it lol

the first part is this:
cos^2 C + sin^2 C = 1
cos ^2 C = 1/4
sin^2 C = 1 - 1/4 = 3/4
sin C = root(3) / 2 = pi / 3 (Im not sure, double check on calculator)
and then depending on the range, there are certain other answers, i think you can do it from here.

second part:
tan D = 5sin D
sin D / cos D = 5 sin D
sinD / sind D = 5 cos D
cos D = 1/5
and calculate this on your calculator
i hope this helps)
6. (Original post by vahik92)
awwwwwwwww, its been about 7 months since i didnt do any maths, i miss it lol

the first part is this:
cos^2 C + sin^2 C = 1
cos ^2 C = 1/4
sin^2 C = 1 - 1/4 = 3/4
sin C = root(3) / 2 = pi / 3 (Im not sure, double check on calculator)
and then depending on the range, there are certain other answers, i think you can do it from here.

second part:
tan D = 5sin D
sin D / cos D = 5 sin D
sinD / sind D = 5 cos D
cos D = 1/5
and calculate this on your calculator
i hope this helps)
I see Thanks for the help For the second part, once you get cos D = 1/5, you calculate D to be 78.46 degrees, but the answers at the back say that you should get 78.46 (which I have got), -78.46 and 0. Any idea how to get the other 2 answers?
7. (Original post by TimmonaPortella)
you get by looking at your graph of and figuring out that there is another value C for which
I'm assuming somewhere in the question it says

for b, I'd try to find a value D for which both sind and tand = 0. because then 5sind and tand will = 0.
I am asking how to do it without a graph And nope, in the question it just says "all possible values". And oh right you are right there
I am asking how to do it without a graph And nope, in the question it just says "all possible values". And oh right you are right there
oh no, actually what am I thinking, C doesn't need confining
I apologise.

and really, you should just be able to sketch out a graph of y=cosx. though you needn't actually use it for that question, you should just know that and that
9. (Original post by TimmonaPortella)
oh no, actually what am I thinking, C doesn't need confining
I apologise.

and really, you should just be able to sketch out a graph of y=cosx. though you needn't actually use it for that question, you should just know that and that
Oh right I see So for the final value you would do 360 - 60 = 300, and then sin 300 = - root 3/2 ?
I see Thanks for the help For the second part, once you get cos D = 1/5, you calculate D to be 78.46 degrees, but the answers at the back say that you should get 78.46 (which I have got), -78.46 and 0. Any idea how to get the other 2 answers?
erm, i know how to get -78.46 , cos X = cos (-X) for any value of X, i.e. cos 78.46 = cos (-78.46).
but for 0, i dont know ( for 0, cos X = 1, which we didnt get, we got cos X = 1/5.. sorry
11. (Original post by vahik92)
erm, i know how to get -78.46 , cos X = cos (-X) for any value of X, i.e. cos 78.46 = cos (-78.46).
but for 0, i dont know ( for 0, cos X = 1, which we didnt get, we got cos X = 1/5.. sorry
Oh right so is cos X = cos (-X) a general rule which only applies for cos?
Oh right so is cos X = cos (-X) a general rule which only applies for cos?
yep, cos x = cos -x for all the values of x. these are all basic things which you should really know for C2 and you will have to use for C3 and C4,, make sure u learn these formulaes as there are quite a lot of them, without them you wont be able to get good grades .. just an advice
13. (Original post by mathz)
for c2 you only learn 2 things:

cos^2 x + sin^2 x =1

tanx=(sinx)/(cosx)

sin is postive for angles between 0 and 180 and negative 180< to 360, cos is positive for angles 0 to 90 and 270 to 360 negative 90-270

use these in a) and b) in a way you think helps you the most.......
This Get used to the basics of trig now..it gets harder at A2..once youve got these basics (ie learning how to solve sinx = a, cosx = a, tanx = a (ie sin-1(a) = x, then using a cast diagram) will help a lot..also learn to use sin^2(x)+cos^2(x) = 1 and (sinx)(cosx) = tanx will help you a lot..and once you learn these it isnt that bad, honest!

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Updated: December 2, 2010
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