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C3 Mixed Exercise 7F Q9 watch

1. 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!
2. (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!
3. sin(θ) = cos(90-θ)
cos(θ) = sin(90 - θ)
4. (Original post by TeeEm)
Well for C I started by using the addition formulae to expand, but was just left with nothing. And nothing for D
5. sin(x+50) = cos(x+40)
So -tan(x+40) = 0
6. (Original post by NotNotBatman)
sin(θ) = cos(90-θ)
cos(θ) = sin(90 - θ)
Where does this come from?
7. (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?
8. (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?
9. (Original post by TeeEm)
does post 3 help?
Youre trying too much
10. (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.
11. (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
12. (Original post by GeologyMaths)
Youre trying too much
I don't think that your solution works, or makes sense...
13. (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
14. (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
15. (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
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!
16. (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
17. (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)
18. (Original post by BenRichi_)
I don't think that your solution works, or makes sense...
this person has been trolling the maths forum today.
19. (Original post by the bear)
this person has been trolling the maths forum today.
how?

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