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C3 Mixed Exercise 7F Q9

Hi,

I was wondering if anybody could help me, I am stuck on C3 Mixed Exercise 7F, Question 9 c and d.

C - solve
sin(θ+40°) + sin(θ+50°) = 0 , 0 ≤ θ ≤ 360°

D - solve
sin² θ/2 = 2sinθ ,0 ≤ θ ≤ 360°

Any help would be appreciated as Physics and Math Tutors Solution jump around and don't really explain anything, which is annoying...

Thanks!
Reply 1
Avatar for TeeEm
TeeEm
19
Original post by BenRichi_
Hi,

I was wondering if anybody could help me, I am stuck on C3 Mixed Exercise 7F, Question 9 c and d.

C - solve
sin(θ+40°) + sin(θ+50°) = 0 , 0 ≤ θ ≤ 360°

D - solve
sin² θ/2 = 2sinθ ,0 ≤ θ ≤ 360°

Any help would be appreciated as Physics and Math Tutors Solution jump around and don't really explain anything, which is annoying...

Thanks!


have you made any start?
sin(θ) = cos(90-θ)
cos(θ) = sin(90 - θ)
Reply 3
Avatar for BenRichi_
BenRichi_
OP
1
Original post by TeeEm
have you made any start?


Well for C I started by using the addition formulae to expand, but was just left with nothing. And nothing for D
sin(x+50) = cos(x+40)
So -tan(x+40) = 0
Reply 5
Avatar for BenRichi_
BenRichi_
OP
1
Original post by NotNotBatman
sin(θ) = cos(90-θ)
cos(θ) = sin(90 - θ)


Where does this come from?
Reply 6
Avatar for TeeEm
TeeEm
19
Original post by BenRichi_
Well for C I started by using the addition formulae to expand, but was just left with nothing. And nothing for D


does post 3 help?
Reply 7
Avatar for BenRichi_
BenRichi_
OP
1
Original post by TeeEm
does post 3 help?


Well I understand how I would use it, but don't understand where that is from, I have never seen this before?
Original post by TeeEm
does post 3 help?


Youre trying too much
Original post by BenRichi_
Where does this come from?


It's taught in c2. Draw a right angled triangle with an angle marked x, so the other angle will have to be 90-x and you'll see that it works.

or consider the cosine and sine graphs.
Reply 10
Avatar for TeeEm
TeeEm
19
Original post by BenRichi_
Well I understand how I would use it, but don't understand where that is from, I have never seen this before?


standard result taught at C2
Reply 11
Avatar for BenRichi_
BenRichi_
OP
1
Original post by GeologyMaths
Youre trying too much


I don't think that your solution works, or makes sense...
Original post by BenRichi_
Well I understand how I would use it, but don't understand where that is from, I have never seen this before?


cos(x) = sin(90-x)
cos(x) = sin90cosx - sinxcos90
cos(x) = cos(x) - 0
Original post by BenRichi_
Hi,

I was wondering if anybody could help me, I am stuck on C3 Mixed Exercise 7F, Question 9 c and d.

C - solve
sin(θ+40°) + sin(θ+50°) = 0 , 0 ≤ θ ≤ 360°

D - solve
sin² θ/2 = 2sinθ ,0 ≤ θ ≤ 360°

Any help would be appreciated as Physics and Math Tutors Solution jump around and don't really explain anything, which is annoying...

Thanks!


Have u come across the factor formula? if not it is
sinp+ sinq== 2sin(p+q/2)cos(p-q/2).... with p as 40° and q as 50°. Sub in values
and you should come to 2sin(θ+45)=0 and cos(-5)=0 where cos(-5) is invalid therefore solve 2sin(θ+45)=0......................ok and tell me what you get :smile:
Reply 14
Avatar for BenRichi_
BenRichi_
OP
1
Original post by raman_17
Have u come across the factor formula? if not it is
sinp+ sinq== 2sin(p+q/2)cos(p-q/2).... with p as 40° and q as 50°. Sub in values
and you should come to 2sin(θ+45)=0 and cos(-5)=0 where cos(-5) is invalid therefore solve 2sin(θ+45)=0......................ok and tell me what you get :smile:


Thank you very much raman, I was just looking through the C3 book and found this, its the best solution and gives the correct answer!
Original post by BenRichi_
Thank you very much raman, I was just looking through the C3 book and found this, its the best solution and gives the correct answer!


no worries :smile:
Original post by BenRichi_
Hi,

I was wondering if anybody could help me, I am stuck on C3 Mixed Exercise 7F, Question 9 c and d.

C - solve
sin(θ+40°) + sin(θ+50°) = 0 , 0 ≤ θ ≤ 360°

D - solve
sin² θ/2 = 2sinθ ,0 ≤ θ ≤ 360°

Any help would be appreciated as Physics and Math Tutors Solution jump around and don't really explain anything, which is annoying...

Thanks!


sin(x)=2sin(x/2)cos(x/2)
Original post by BenRichi_
I don't think that your solution works, or makes sense...


this person has been trolling the maths forum today.
Original post by the bear
this person has been trolling the maths forum today.


how?

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