Ken Poison
Badges: 6
Rep:
?
#1
Report Thread starter 3 weeks ago
#1
Hi I am very bad at trigonometry and I don’t understand questions 9d to 9g

Please could someone explain how do do these?

Thanks Name:  39A9C2D1-D89B-4CB0-A361-AE0BE0D13878.jpg.jpeg
Views: 10
Size:  26.8 KB
0
reply
the bear
Badges: 20
Rep:
?
#2
Report 3 weeks ago
#2
sin2Θ can be written as 2sinΘcosΘ

similarly sinΘ can be written as 2sin(Θ/2)cos(Θ/2)
0
reply
simon0
Badges: 13
Rep:
?
#3
Report 3 weeks ago
#3
For the other questions, for:
e) Try the R-fomulas,
f) Try the sum-product formula,
g) Perhaps a disguised quadratic?
0
reply
Ken Poison
Badges: 6
Rep:
?
#4
Report Thread starter 3 weeks ago
#4
(Original post by simon0)
For the other questions, for:
e) Try the R-fomulas,
f) Try the sum-product formula,
g) Perhaps a disguised quadratic?
thank you , i am just struggling on 9f still, i dont know how to do that , thanks
0
reply
Ken Poison
Badges: 6
Rep:
?
#5
Report Thread starter 3 weeks ago
#5
(Original post by the bear)
sin2Θ can be written as 2sinΘcosΘ

similarly sinΘ can be written as 2sin(Θ/2)cos(Θ/2)
thank you
0
reply
the bear
Badges: 20
Rep:
?
#6
Report 3 weeks ago
#6
for f) you can use one of these formulae:

Name:  tsrtrigidents.png
Views: 16
Size:  62.5 KB
0
reply
simon0
Badges: 13
Rep:
?
#7
Report 3 weeks ago
#7
How did it go?
0
reply
Ken Poison
Badges: 6
Rep:
?
#8
Report Thread starter 3 weeks ago
#8
(Original post by the bear)
for f) you can use one of these formulae:

Name:  tsrtrigidents.png
Views: 16
Size:  62.5 KB
I don’t think I have learnt it before I will check it up at school , thanks
0
reply
Kane M. Gordon
Badges: 4
Rep:
?
#9
Report 3 weeks ago
#9
Is this A-Level ? , becauase this level of trigonemetry definitely isn't on Edexcel Mathematics and I'm in top set amd have never seen it.
0
reply
alevel1232
Badges: 9
Rep:
?
#10
Report 3 weeks ago
#10
(Original post by Kane M. Gordon)
Is this A-Level ? , becauase this level of trigonemetry definitely isn't on Edexcel Mathematics and I'm in top set amd have never seen it.
Yeah some of the questions they put in the textbook are much weirder and harder compared to questions
on actual papers.
0
reply
simon0
Badges: 13
Rep:
?
#11
Report 3 weeks ago
#11
(Original post by Ken Poison)
I don’t think I have learnt it before I will check it up at school , thanks
They are in the formula booklet (at least for Edexcel) however, they can also be derived.

We know:

 \circ \, \, \cos (a+b) = \cos (a) \cos (b) - \sin (a) \sin (b) ,


 \circ \, \, \cos (a-b) = \cos (a) \cos (b) + \sin (a) \sin (b).


Then just subtract the terms:


 \cos (a+b) - \cos (a - b),

 = [ \cos (a) \cos (b) - \sin(a) \sin(b) ] - [ \cos (a) \cos (b) + \sin (a) \sin (b) ],

 = -2 \sin (a) \sin(b) .
Last edited by simon0; 3 weeks ago
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

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

Personalise

University open days

  • Bournemouth University
    Midwifery Open Day at Portsmouth Campus Undergraduate
    Wed, 18 Dec '19
  • The University of Law
    Open Day – GDL and LPC - Chester campus Postgraduate
    Sat, 4 Jan '20
  • University of East Anglia
    Mini Open Day Undergraduate
    Mon, 6 Jan '20

Have you voted in today's general election?

Yes (176)
48.75%
No (44)
12.19%
I'm not old enough (141)
39.06%

Watched Threads

View All