# Help Proving An Identity [A2 Core 3]Watch

#1
I'm having some issues doing this question with proving an identity it's the first of this type of question i've ever seen and was wondering how i would go about doing it i've had an attempt.

Question

My Working

This is where i get stuck im quite unsure what to do here!
0
10 years ago
#2
u sure its not cosec^2x+cot^2x?

0
10 years ago
#3
(Original post by Kevlar)
I'm having some issues doing this question with proving an identity it's the first of this type of question i've ever seen and was wondering how i would go about doing it i've had an attempt.

Question

My Working

This is where i get stuck im quite unsure what to do here!

there is an easier way :

LHS:

1/sin^2thetha - 1/tan^2 thetha

1/sin^thetha - cos^2thetha/sin^2 thetha

taking sin^2thetha as the common denominator :

(1-cos^2 thetha)/sin^2 thetha

I think on the RHS, it should be (1-cos^2 thetha)/sin&^2thetha
0
10 years ago
#4
You've got a plus or minus sign wrong somewhere. Divide both the terms in the RHS's numerator by the denominator, and a slightly different version of the identity pops out immediately.
#5
oh i was using

not

0
10 years ago
#6
(Original post by Kevlar)
eh :s im confused lolz

cosec = 1/sin
and
cot = 1/tan

hence using that
LHS:

cosec^2 thetha - cot^2 thetha

1/sin^2thetha - 1/tan^2 thetha ; now u knoe that tan= sin/cos hence 1/tan = cos/sin

1/sin^thetha - cos^2thetha/sin^2 thetha

taking sin^2thetha as the common denominator :

(1-cos^2 thetha)/sin^2 thetha

and as i said, the RHS, it should be (1-cos^2 thetha)/sin&^2thetha
0
10 years ago
#7
(Original post by Kevlar)
oh i was using

not

thts rite

and cosec= 1/sin
0
10 years ago
#8
the trick is to look at the 3rd letter :

cosec = 1/sin

sec = 1/cos

cot = 1/tan

and u knoe from c2 that tan= sin/cos

hence 1/tan = 1/sin/cos = cos/sin
0
#9
(Original post by wizz_kid)
cosec = 1/sin
and
cot = 1/tan

hence using that
LHS:

cosec^2 thetha - cot^2 thetha

1/sin^2thetha - 1/tan^2 thetha ; now u knoe that tan= sin/cos hence 1/tan = cos/sin

1/sin^thetha - cos^2thetha/sin^2 thetha

taking sin^2thetha as the common denominator :

(1-cos^2 thetha)/sin^2 thetha

and as i said, the RHS, it should be (1-cos^2 thetha)/sin&^2thetha
I get what your saying but the RHS of the equation is definately correct it is (1+cos^2 theta)/sin^2theta

not 1-cos^2 unless there was a printing error on the question sheet which i highly doubt...
0
10 years ago
#10
(Original post by Kevlar)
I get what your saying but the RHS of the equation is definately correct it is (1+cos^2 theta)/sin^2theta

not 1-cos^2 unless there was a printing error on the question sheet which i highly doubt...

hmmm what about the LHS? is it cosec^2 thetha + cot^2 thetha ?
0
10 years ago
#11
look you morons. There is a mistake in the paper it should be a plus.

if it isn't then you get
0
#12
(Original post by wizz_kid)
hmmm what about the LHS? is it cosec^2 thetha + cot^2 thetha ?
no its cosec^2 theta - cot^2 theta
0
10 years ago
#13
(Original post by Totally Tom)
There is a mistake in the paper it should be a plus.
agreed
0
10 years ago
#14
(Original post by Kevlar)
no its cosec^2 theta - cot^2 theta

it cant be!

coz :

cosec^2 theta - cot^2 theta

= 1 + cot^2 thetha - cot^2 thetha

yea

and the cot's cancel out ..which leaves u with 1
0
#15
(Original post by wizz_kid)
it cant be!

coz :

cosec^2 theta - cot^2 theta

= 1 + cot^2 thetha - cot^2 thetha

yea

and the cot's cancel out ..which leaves u with 1
so can someone show me the working if the question was

0
10 years ago
#16
(Original post by Kevlar)
so can someone show me the working if the question was

yea

LHS:

1/sin^2thetha + 1/tan^2 thetha

1/sin^thetha + cos^2thetha/sin^2 thetha

taking sin^2thetha as the common denominator :

(1+cos^2 thetha)/sin^2 thetha
0
#17
Thank you all for your help much appreciated, stupid teachers typed the question wrong lol
0
10 years ago
#18
(Original post by Kevlar)
Thank you all for your help much appreciated, stupid teachers typed the question wrong lol

no problem as long as u understand whts going on
0
#19
yeah i see whats going on i'll have to look for more types of this question and get some practice x]
0
10 years ago
#20
(Original post by Kevlar)
yeah i see whats going on i'll have to look for more types of this question and get some practice x]

yea and do some delphis papers ...they are challenging but very helpful
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 (864)
80.3%
Leave (212)
19.7%