C3 trig help
I've tried this question twice and it should be fairly easy but I keep getting it wrong :/
cos2x = 1 - cosx
I originally put all the cosx on one side then factorised by taking out cos. that didn't work so I replaced cos2x with 2cos^2x-1 to form a quadratic which also didn't end in the correct answer :/
Posted from TSR Mobile
cos2x = 1 - cosx
I originally put all the cosx on one side then factorised by taking out cos. that didn't work so I replaced cos2x with 2cos^2x-1 to form a quadratic which also didn't end in the correct answer :/
Posted from TSR Mobile
Original post by kendellex
I've tried this question twice and it should be fairly easy but I keep getting it wrong :/
cos2x = 1 - cosx
I originally put all the cosx on one side then factorised by taking out cos. that didn't work so I replaced cos2x with 2cos^2x-1 to form a quadratic which also didn't end in the correct answer :/
Posted from TSR Mobile
cos2x = 1 - cosx
I originally put all the cosx on one side then factorised by taking out cos. that didn't work so I replaced cos2x with 2cos^2x-1 to form a quadratic which also didn't end in the correct answer :/
Posted from TSR Mobile
What was your quadratic?
Original post by m4ths/maths247
What was your quadratic?
I thought it was 2y^2 + y - 2 = 0 were y = cosx. It doesn't produce the correct answer though so must be wrong
Posted from TSR Mobile
Original post by krisshP
Cos2x=1-cosx
Let x=45
Cos90=1-cos45
0=1-1/√2
LHS≠RHS
So cos2x≠1-cosx
Let x=45
Cos90=1-cos45
0=1-1/√2
LHS≠RHS
So cos2x≠1-cosx
I'm not sure what you are trying to do here?
Original post by kendellex
I thought it was 2y^2 + y - 2 = 0 were y = cosx. It doesn't produce the correct answer though so must be wrong
Posted from TSR Mobile
Posted from TSR Mobile
Answer or answers?
What is your interval?
Have you solved for x and not cosx?
There are certainly 2 solutions between 0 and 2pi
2 cos^2(x) - 1 =1 - cosx
2 cos^2(x) + cosx - 2 =0
cosx= (1+/− (1-4(2)(-2))^1/2)4 (quadratic equation)
= (1+/−3)/4
cosx= 1 OR -1/2
Therefore x= 0.54 rad or 0.88 rad
2 cos^2(x) + cosx - 2 =0
cosx= (1+/− (1-4(2)(-2))^1/2)4 (quadratic equation)
= (1+/−3)/4
cosx= 1 OR -1/2
Therefore x= 0.54 rad or 0.88 rad
Original post by tsumannai
2 cos^2(x) - 1 =1 - cosx
2 cos^2(x) + cosx - 2 =0
cosx= (1+/− (1-4(2)(-2))^1/2)4 (quadratic equation)
= (1+/−3)/4
cosx= 1 OR -1/2
Therefore x= 0.54 rad or 0.88 rad
2 cos^2(x) + cosx - 2 =0
cosx= (1+/− (1-4(2)(-2))^1/2)4 (quadratic equation)
= (1+/−3)/4
cosx= 1 OR -1/2
Therefore x= 0.54 rad or 0.88 rad
The board etiquette is such that full solutions are not posted.
This has not answered the question anyhow....
Original post by m4ths/maths247
I'm not sure what you are trying to do here?
Oh no, sorry, I thought that we were supposed to prove that cos2x is identically equal to 1-cosx, now I realise we're we're solving cos2x=1-cosx after looking at post 7. After all there are many trig questions based on proving.
Quick Reply
Related discussions
- Edexcel A2 Mathematics: Core Mathematics C4 6666 01 - 22 June 2018 [Exam Discussion]
- Maths Trig question
- C3 Trig question
- A Level Maths Integration
- AQA A-level Further Maths Required Trig Functions?
- Applied Calculus Help
- Further maths: Further Calculus
- Help urgent maths
- Help how do I get this answer maths
- AS Maths edexcel 2023
- Struggling with Year 2 pure maths
- Maths Question
- Advanced mathematics
- AS level physics forces and motion question
- maths help
- Help with complex summation further maths a levels
- edexcel maths a level
- GCSE Edexcel Maths - trigonometric ratios of angles between 0 and 360
- What topics are NOT in the non calculator paper in GCSE maths?
- Help urgently maths
Latest
Trending
Last reply 3 days ago
Did Cambridge maths students find maths and further maths a level very easy?Last reply 2 weeks ago
Edexcel A Level Mathematics Paper 2 unofficial mark scheme correct me if wrongMaths
71
Trending
Last reply 3 days ago
Did Cambridge maths students find maths and further maths a level very easy?Last reply 2 weeks ago
Edexcel A Level Mathematics Paper 2 unofficial mark scheme correct me if wrongMaths
71
