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secondary 4 | A Maths
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Kathy
Kathy

secondary 4 chevron_right A Maths chevron_right Singapore

Thank u

Date Posted: 4 years ago
Views: 355
C Meen
C Meen
4 years ago
Which question are you asking?
Eric Nicholas K
Eric Nicholas K
4 years ago
Seen, will do all later
C Meen
C Meen
4 years ago
Eric, should we let Kathy attempt the questions first?
Eric Nicholas K
Eric Nicholas K
4 years ago
I think it’s alright, I will just do the questions as usual. But I will do bit by bit.

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Jiayang
Jiayang's answer
1883 answers (Tutor Details)
1st
Eric Nicholas K
Eric Nicholas K
4 years ago
Q38 has slight error in the expansion. I have corrected it accordingly.
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Eric Nicholas K
Eric Nicholas K's answer
5997 answers (Tutor Details)
Q28
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Eric Nicholas K
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5997 answers (Tutor Details)
Q29
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Eric Nicholas K
Eric Nicholas K's answer
5997 answers (Tutor Details)
Q30
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Eric Nicholas K
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5997 answers (Tutor Details)
Q31
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Eric Nicholas K
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5997 answers (Tutor Details)
Q32
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Eric Nicholas K
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5997 answers (Tutor Details)
Q33

End of session.
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Eric Nicholas K
Eric Nicholas K's answer
5997 answers (Tutor Details)
Q34a, Q34b

I always change all sad face graphs to smiley face graphs so I only need to remember one kind of graph. In other words, I make sure one side is zero and the other side has a positive coefficient of x2.
Kathy
Kathy
4 years ago
How or when will I know to draw the line outside or inside the u shape
Eric Nicholas K
Eric Nicholas K
4 years ago
For your discriminants b2 - 4ac which reduce to inequalities such as this one, the graph of the b2 - 4ac (to be distinguished from the graph of the actual curve) must cut the “horizontal axis”.
Eric Nicholas K
Eric Nicholas K
4 years ago
So let’s say you obtain k2 - 2k - 3 > 0 as the inequality and you are solving for it.

This graph will definitely cut the horizontal 0, so we factorise into (k - 3) (k + 1) and shade the appropriate region.
Kathy
Kathy
4 years ago
I mean the shade the part
Eric Nicholas K
Eric Nicholas K
4 years ago
Always convert your quadratic inequality into positive coefficients of x2 so you will remember the u-shaped graph only. Remembering the n-shaped graph can cause confusion.
Eric Nicholas K
Eric Nicholas K
4 years ago
Above the horizontal line is the region “> 0”.

Below the horizontal line is the region “< 0”.
Eric Nicholas K
Eric Nicholas K
4 years ago
So let’s say (k - 3) (k + 1) > 0.

We draw the u-shaped graph passing -1 and 3.

The parts above the line (k < -1 and k > 3) are to be shaded, since for these values of k, the value of (k - 3) (k + 1) are positive after substitution of k.
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Eric Nicholas K
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5997 answers (Tutor Details)
Q34c, Q34d
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Eric Nicholas K
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5997 answers (Tutor Details)
Q34e, Q34f
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Eric Nicholas K
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5997 answers (Tutor Details)
Q35
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Eric Nicholas K
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5997 answers (Tutor Details)
Q36, same approach as Q35
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Eric Nicholas K
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5997 answers (Tutor Details)
Q37, Q38