The Student Room Group

Alevel trig maths question help

show that the equation

2tanx(8cosx+23sin^2 x)= 8sin2x(1+tan^2 x )

May be written as
sin2x(Acos^2 x + Bcosx + C) = 0

I managed to get to the last step of working out which is correct on the mark scheme, however I can’t reach the final answer

I got up to
sin2x(8cosx+ 23 - 23cos^2 x ) = 8sin2x

The markscheme answer is
sin2x(23cos^2 x - 8cosx -15) = 0

I can’t seem to manipulate my answer to this
Any help pls??
Reply 1
Original post by harlz_chalamet
show that the equation
2tanx(8cosx+23sin^2 x)= 8sin2x(1+tan^2 x )
May be written as
sin2x(Acos^2 x + Bcosx + C) = 0
I managed to get to the last step of working out which is correct on the mark scheme, however I can’t reach the final answer
I got up to
sin2x(8cosx+ 23 - 23cos^2 x ) = 8sin2x
The markscheme answer is
sin2x(23cos^2 x - 8cosx -15) = 0
I can’t seem to manipulate my answer to this
Any help pls??

Take the left hand side over to the right and ...
Original post by harlz_chalamet
show that the equation
2tanx(8cosx+23sin^2 x)= 8sin2x(1+tan^2 x )
May be written as
sin2x(Acos^2 x + Bcosx + C) = 0
I managed to get to the last step of working out which is correct on the mark scheme, however I can’t reach the final answer
I got up to
sin2x(8cosx+ 23 - 23cos^2 x ) = 8sin2x
The markscheme answer is
sin2x(23cos^2 x - 8cosx -15) = 0
I can’t seem to manipulate my answer to this
Any help pls??
Get the 8sin2x to the left and factorize sin2x. That will give you 23-8 which is 15 with everything else the same.
Reply 3
Original post by math-path
Here is what it looks like:
Screenshot 2024-05-24 195020.png

Probably worth just offering hints/help rather than posting full solutions
https://www.thestudentroom.co.uk/showthread.php?t=4919248
Original post by mqb2766
Probably worth just offering hints/help rather than posting full solutions
https://www.thestudentroom.co.uk/showthread.php?t=4919248

You provided pretty much every direction the student needed so I decided to show all steps for other students that might be reading this post, just for complete closure.
Original post by math-path
You provided pretty much every direction the student needed so I decided to show all steps for other students that might be reading this post, just for complete closure.

Was helpful for me so thank u!
Reply 6
Original post by math-path
You provided pretty much every direction the student needed so I decided to show all steps for other students that might be reading this post, just for complete closure.

Thats pretty much covered in the link about not expecting full solutions, whether its the OP or not. If another person still cannot do it, they can ask.
Original post by mqb2766
Thats pretty much covered in the link about not expecting full solutions, whether its the OP or not. If another person still cannot do it, they can ask.

OK

Quick Reply