# maths C2 trig help!

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#1
Hi, I'm stuck on a few trig eq. Q out the textbook;

Solve the equation 3sin^2x=1+5cosx in the range 0-180

Solve the equation cos(3x-pi)=-1

I understand everything else I just need help in rearranging the equations (possibly using the identities) to find x! I can't quite get it right, help would be appreciated, ty.
-A
0
4 years ago
#2
(Original post by anton6846)
Hi, I'm stuck on a few trig eq. Q out the textbook;

Solve the equation 3sin^2x=1+5cosx in the range 0-180

Solve the equation cos(3x-pi)=-1

I understand everything else I just need help in rearranging the equations (possibly using the identities) to find x! I can't quite get it right, help would be appreciated, ty.
-A
If you want help rearranging, just post your attempt at the rearrangement and we'll tell you exactly where the errors lie.
1
4 years ago
#3
(Original post by anton6846)
Hi, I'm stuck on a few trig eq. Q out the textbook;

Solve the equation 3sin^2x=1+5cosx in the range 0-180

Solve the equation cos(3x-pi)=-1

I understand everything else I just need help in rearranging the equations (possibly using the identities) to find x! I can't quite get it right, help would be appreciated, ty.
-A
For the first one, have you tried expressing sin2x in terms of cosx? Think about identities.
0
#4
(Original post by RDKGames)
If you want help rearranging, just post your attempt at the rearrangement and we'll tell you exactly where the errors lie.
Well I've moved pi to the RHS and divided by 3 but I know this is wrong?

(Original post by TheMindGarage)
For the first one, have you tried expressing sin2x in terms of cosx? Think about identities.
o ya thanks ill give it a go.
0
4 years ago
#5
(Original post by anton6846)
Well I've moved pi to the RHS and divided by 3 but I know this is wrong?
Seems like a valid portion of the full procedure. Must be going wrong elsewhere if you can't get the correct answer.
0
4 years ago
#6
you must learn these:

https://mathsteaching.wordpress.com/...ic-identities/
0
4 years ago
#7
(Original post by anton6846)
Hi, I'm stuck on a few trig eq. Q out the textbook;

Solve the equation 3sin^2x=1+5cosx in the range 0-180

Solve the equation cos(3x-pi)=-1

I understand everything else I just need help in rearranging the equations (possibly using the identities) to find x! I can't quite get it right, help would be appreciated, ty.
-A
The first one needs to be converted into a quadratic in cos(x) first. You can inverse cos both sides of the second but you will need to extend the interval to get all solutions. There are two examples just like this at this link:
http://studywell.com/maths/pure-math...ric-equations/
Hope that helps.
0
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