Hard Trig Qs

#1

Can someone please explain that first line to me - I feel like I'm being rly stupid.
0
1 month ago
#2

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
1 month ago
#3

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
#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
#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
1 month ago
#6
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
#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
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