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Trigonometric Equation (HARD)

in the title

IMAGE.jpg

Help!!!

Spoiler

is that a C3 question?
Reply 2
Avatar for TeeEm
TeeEm
OP
19
It would have been if and only if I was allowed to write the C3 paper.
Equivalent to sin(16x)+sin(2x)=0sin(16x) + sin(2x) = 0

I don't know if that's going to help me.
(edited 8 years ago)
Reply 4
Avatar for TeeEm
TeeEm
OP
19
Original post by EricPiphany
Equivalent to sin(16x)+sin(2x)=0sin(16x) + sin(2x) = 0

I dont know if that's going to help me.


the answer is definitely to both
Original post by TeeEm
the answer is definitely to both


OK, I think I've got it.
sin(9x)=0,cos(7x)=0sin(9x) = 0, cos(7x) = 0
Reply 6
Avatar for TeeEm
TeeEm
OP
19
Original post by EricPiphany
OK, I think I've got it.
sin(9x)=0,cos(7x)=0sin(9x) = 0, cos(7x) = 0


I think it can be done this way

(looking at the form of the answers you did not picked the most efficient way but it looks good.)

Please let some body else try
Original post by TeeEm
I think it can be done this way

(looking at the form of the answers you did not picked the most efficient way but it looks good.)

Please let some body else try


Ok, fine.
Reply 8
Avatar for Marxist
Marxist
10
Original post by TeeEm
in the title

IMAGE.jpg

Help!!!

Spoiler



If I let 2x=theta, do you think it will work out nicely or become a bit more tedious?

Edit: Hmmm... let me try.
Reply 9
Avatar for TeeEm
TeeEm
OP
19
Original post by Marxist
If I let 2x=theta, do you think it will work out nicely or become a bit more tedious?

Edit: Hmmm... let me try.


I cannot tell unless I try
Original post by TeeEm
I cannot tell unless I try

:P
Reply 11
Avatar for TeeEm
TeeEm
OP
19
Original post by TeeEm
in the title

IMAGE.jpg

Help!!!

Spoiler





and here is my solution
sp_p_18.jpg374.3KB
Reply 12
Avatar for to4ka
to4ka
3
8cos(2x)cos(4x)cos(8x)=-1
First check if x=0 and x=pi÷2 are solutions.
Multiplying both sides by sin(2x) /hence the check; multiplying both sides by 0 isn't allowed/:
LHS = 4 * 2sin(2x)cos(2x)cos(4x)cos(8x)
= 2 * 2sin(4x)cos(4x)cos(8x)
= 2sin(8x)cos(8x)
= sin(16x)
RHS = -sin(2x) = sin(-2x)

sin(16x)=sin(-2x)
16x = -2x + 2k*pi OR 16x = pi + 2x + 2k*pi

continue...

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Oh my.. that is a very elegant solution.

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