Hard Trig Qs

Watch this thread
GradeKing99
Badges: 4
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#1
Report Thread starter 1 month ago
#1
Name:  WhatsApp Image 2022-05-20 at 9.16.42 PM.jpeg
Views: 16
Size:  108.0 KB

Can someone please explain that first line to me - I feel like I'm being rly stupid.
0
reply
cm.22
Badges: 12
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#2
Report 1 month ago
#2
(Original post by GradeKing99)
Name:  WhatsApp Image 2022-05-20 at 9.16.42 PM.jpeg
Views: 16
Size:  108.0 KB

Can someone please explain that first line to me - I feel like I'm being rly stupid.
Hi, If I remember correctly, you might have to use the double angle formula/identities.
OR you might need to sub in the values that are under the box you drew e.g. sin(x) = 1/2, in to the equations in the box.
Hope that helps
Last edited by cm.22; 1 month ago
0
reply
Mugiwara!!
Badges: 8
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#3
Report 1 month ago
#3
(Original post by GradeKing99)
Name:  WhatsApp Image 2022-05-20 at 9.16.42 PM.jpeg
Views: 16
Size:  108.0 KB

Can someone please explain that first line to me - I feel like I'm being rly stupid.
As said before me, you will have to use double angle identities.
If you also look at cos (3x) it can be written as cos(2x + x) and now you can also use the cos(A+B) rule as well.
Harder Questions like these will definitely try to include both sets of identities in one question. Hope this helps !
0
reply
GradeKing99
Badges: 4
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#4
Report Thread starter 1 month ago
#4
4

(Original post by Mugiwara!!)
As said before me, you will have to use double angle identities.
If you also look at cos (3x) it can be written as cos(2x + x) and now you can also use the cos(A+B) rule as well.
Harder Questions like these will definitely try to include both sets of identities in one question. Hope this helps !
trust me - i tried multiple ways of doing this, and I am still really stuck. Could you provide further advice on next steps?
0
reply
GradeKing99
Badges: 4
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#5
Report Thread starter 1 month ago
#5
(Original post by cm.22)
Hi, If I remember correctly, you might have to use the double angle formula/identities.
OR you might need to sub in the values that are under the box you drew e.g. sin(x) = 1/2, in to the equations in the box.
Hope that helps
Anything else after that? Subbing in the values is for a different question
0
reply
mqb2766
Badges: 19
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#6
Report 1 month ago
#6
(Original post by GradeKing99)
Anything else after that? Subbing in the values is for a different question
Going from line 1 to 2 is the product to sum (sum to product) trig identity
https://www.cliffsnotes.com/study-gu...uct-identities
with alpha=2theta, beta=theta.

If necessary you could do it the "long" way (prove the formula) by expanding
cos(3theta) = cos(2theta + theta) = ...
cos(theta) = cos(2theta - theta) = ...
using the angle sum identities and subtracting, but if youve covered the product to sum/sum to product identities then its just quoting the relevant one.
Last edited by mqb2766; 1 month ago
0
reply
GradeKing99
Badges: 4
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#7
Report Thread starter 1 month ago
#7
(Original post by mqb2766)
Going from line 1 to 2 is the product to sum (sum to product) trig identity
https://www.cliffsnotes.com/study-gu...uct-identities
with alpha=2theta, beta=theta.

If necessary you could do it the "long" way (prove the formula) by expanding
cos(3theta) = cos(2theta + theta) = ...
cos(theta) = cos(2theta - theta) = ...
using the angle sum identities and subtracting, but if youve covered the product to sum/sum to product identities then its just quoting the relevant one.
Thanks sm! I wasn't aware of this concept
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Year 12s - where are you at with making decisions about university?

I’ve chosen my course and my university (19)
32.2%
I’ve chosen my course and shortlisted some universities (22)
37.29%
I’ve chosen my course, but not any universities (2)
3.39%
I’ve chosen my university, but not my course (3)
5.08%
I’ve shortlisted some universities, but not my course (4)
6.78%
I’m starting to consider my university options (7)
11.86%
I haven’t started thinking about university yet (1)
1.69%
I’m not planning on going to university (1)
1.69%

Watched Threads

View All