Jul/09

O Level A-Math Trigonometry Basics : How Do We Know Which Formula To Use?

16 Comments · Posted by alwaysLovely in A-Math, Reader Question

For the past month, other than being busy with the June Intensive Revision Programmes, I was also packed with Mid Year Exam Papers Review for my group of students.

I am pleased to announce that almost all see an improvement in their Mid Year Results (One boy has his grades jump from F9 to A2! Congrats, B!)

I was reviewing the school a-Math exam papers with one of my students during my A-Math Ultimate Leap Programme when she posted me a good question.

Let’s take a look at her Trigonometry question first:

This was her solution for the question:

There is one misconception in her thoughts, can you spot it?

sin 3x is not equal to sin x + sin 2x!

In fact, the correct formula to choose for this question is

sin 3x = sin (2x + x)

= sin2xcosx + cos2xsinx

Her question was: how do you know which formula to use?

TIP: When the angle involved is ODD, we usually use addition formula (just like in this question).

When angle is EVEN, double angle formula is perhaps the correct one to choose.

Are you confused just like my student, which formula should be use? Leave me a comment.

I hope this post has made your understanding clearer :-)

Below is a list of useful posts on A-Math Trigonometry:

PS: I will be re-running A-Math Trigonometry Mastery Workshop in July as some students miss out the one in June due to other commitments. Registration is open! Click here for more details

trigonometry · trigonometry formula · trigonometry workshop

16 comments

Danielle Relation · July 10, 2009 at 2:47 pm

I don’t like math but as i realized, math is very useful in life! too bad that children don’t realize this sooner

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desiree · August 4, 2009 at 6:00 pm

im still confuse…

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alwaysLovely Reply:
August 11th, 2009 at 11:12 am
What are you confused about?

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arun Reply:
February 6th, 2010 at 1:01 pm
i bunked few of ma classes so got doubt in allied angles

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real · August 10, 2009 at 6:11 pm

Wow this was really informative! I didnt know about that haha

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Nguy?n ??c Tùng · August 18, 2009 at 5:20 pm

It is very Useful for me.

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sm · September 11, 2009 at 12:41 am

thanks this came out as a part of a question in my prelim now i noe how to do it =D

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alwaysLovely Reply:
September 11th, 2009 at 7:12 am
I’m glad you know how to do the question now!

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meera · September 24, 2009 at 11:49 pm

modulus graphs – method is so convenient.
thank u very much

Reply
ariane · October 8, 2009 at 10:55 pm

Hi, i am so happy to know you.I want to ask if i can also get information about A-LEVEL maths

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gautam · October 28, 2009 at 4:51 am

i am unable to understand this :(… plz explain in more detail or do it frm the basic plz….

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Pho Tharr · November 27, 2009 at 7:10 pm

It is useful for me! Thanks! Please send me another amazing things.

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Aayush · March 23, 2010 at 5:20 pm

why do i need a o levl maths for admission in a international university

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Joanan S. Sedano · June 4, 2010 at 8:11 am

Hi!! yes.. i was a bit confuse ..through your explaination, it beame clear now

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Darren · July 14, 2010 at 1:36 am

I just don’t know about prove the identity,i don’t understand how could it prove to be useful to our daily life..

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Darren · July 14, 2010 at 1:48 am

i don’t know a bit about rate of change, could someone explain it via the same website??

Reply