# Hi, I’m tuck on a proving trig questionWatch

#1
1- cos2x / cos^2 = tan^2 x
0
1 month ago
#2
Probably tan^2 x + 1 = sec^2 x is useful
0
1 month ago
#3
use cos 2x = 2 cos^2 x -1
then simplify the fraction and use a pythagorean identity
0
1 month ago
#4
or simply cos2x = 1 - sin^2 x
?!
0
1 month ago
#5
(Original post by begbie68)
or simply cos2x = 1 - sin^2 x
?!
um cos 2x = 1 - 2sin^2 x but okay
0
1 month ago
#6
(Original post by BobbJo)
um cos 2x = 1 - 2sin^2 x but okay
ohhhhhh so you mean there's a mishtake in the OP question, too?

should be:
... = 2tan^2(x) ?
0
1 month ago
#7
(Original post by begbie68)
ohhhhhh so you mean there's a mishtake in the OP question, too?

should be:
... = 2tan^2(x) ?
no the OP question is correct

Spoiler:
Show
1 - cos2x/cos^2x= 1 - (2cos^2 x -1)/cos^2 x = 1 - [2 - sec^2x] = sec^2 x -1 = tan^2 x
0
1 month ago
#8
(Original post by BobbJo)
no the OP question is correct

Spoiler:
Show

1 - cos2x/cos^2x= 1 - (2cos^2 x -1)/cos^2 x = 1 - [2 - sec^2x] = sec^2 x -1 = tan^2 x

ok. cheers. I read it as
(1-cos2x)/cos^2(x) = 2sin^2(x) / cos^2(x) = 2tan^2(x)

I'm gonna have to practice LaTex to stop getting confused with some of these types of trigs involving squares and doubles....
0
X

new posts

Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### University open days

• University of East Anglia
All Departments Open 13:00-17:00. Find out more about our diverse range of subject areas and career progression in the Arts & Humanities, Social Sciences, Medicine & Health Sciences, and the Sciences. Postgraduate
Wed, 30 Jan '19
• Aston University
Wed, 30 Jan '19
• Solent University
Sat, 2 Feb '19

### Poll

Join the discussion

Remain (868)
80.07%
Leave (216)
19.93%