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secondary 4 | A Maths
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Kathy
Kathy

secondary 4 chevron_right A Maths chevron_right Singapore

thank you

Date Posted: 4 years ago
Views: 484
Eric Nicholas K
Eric Nicholas K
4 years ago
Seen, later. The other tutor has apparently responded and has done a good job of writing the answer for the other question.
Kathy
Kathy
4 years ago
Ya. Need ur help in more qns de
Kathy
Kathy
4 years ago
Tomorrow I be doing my workbook qns
And starting my revision
Kathy
Kathy
4 years ago
The other qns
The person never help me out with qns 2
Eric Nicholas K
Eric Nicholas K
4 years ago
Will visit the questions again later, but I doubt I can complete all in time as I have classes in the morning tmr.
Kathy
Kathy
4 years ago
Ok. Can
Thank you
Kathy
Kathy
4 years ago
What are the four r formula
Eric Nicholas K
Eric Nicholas K
4 years ago
The one which I wrote down on paper. I summarised it in two equations.
Kathy
Kathy
4 years ago
Thank you
Kathy
Kathy
4 years ago
Tomorrow I send last part of this chapter
I will stop for two days.
I will do math on Thursday
Eric Nicholas K
Eric Nicholas K
4 years ago
Ok starting once I am ready
Kathy
Kathy
4 years ago
Ok

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Eric Nicholas K
Eric Nicholas K's answer
5997 answers (Tutor Details)
1st
Q1, Q2, Q3

Will do the rest another time.
Kathy
Kathy
4 years ago
I still can’t understsnd r formula
Eric Nicholas K
Eric Nicholas K
4 years ago
That formula is a tool to combine an equation containing the sum or difference of sines and cosines. In some situations, say the equation sin x = cos x, we can divide both sides by cos x to obtain tan x = 1. But what happens if say, sin x - cos x = 0.5? We cannot do the same method. One approach, is then, to use the R-formula to combine the sin x and cos x into a single sin or cos.
Eric Nicholas K
Eric Nicholas K
4 years ago
You will need to remember the formulae

a sin x + b cos x = R sin (x + alp)
a sin x - b cos x = R sin (x - alp)
a cos x + b sin x = R cos (x - alp)
a cos x - b sin x = R cos (x + alp)

R = sqrt (a2 + b2), essentially Pythagoras theorem

alp = tan-1 (b/a) and must be an acute angle
Eric Nicholas K
Eric Nicholas K
4 years ago
Depending on which form the question wants you to do, you may need to rearrange the terms.

If the form is R sin (x +- alp), you must put the sin x first before cos x (eg 5 sin x + 2 cos x, not 2 cos x + 5 sin x) as putting the wrong order will get you the wrong order, and hence the wrong angle, for alp.

If the form is R cos (x +- alp), you must put the cos x first before sin x.
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Eric Nicholas K
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5997 answers (Tutor Details)
Q4 to Q5c
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Eric Nicholas K
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5997 answers (Tutor Details)
Q5d to Q7a
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Eric Nicholas K
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5997 answers (Tutor Details)
Q7b to Q10