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secondary 4 | A Maths
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secondary 4 chevron_right A Maths chevron_right Singapore

Good afternoon! How do i do qns 35? Just part i will do :)

Date Posted: 4 months ago
Views: 18
Eric Nicholas K
Eric Nicholas K
4 months ago
Hi Candice! We show that dy/dx < 0 for all x.

Another way is to do long division and reasoning.

y = (16 - 3x) / (x + 3)

= (x + 3) (-3) - (16 - 3x) (1), whole thing divided by (x + 3)^2

= -9 divided by (x + 3)^2

(x + 3)^2 is always non negative but here it cannot equal zero since it is in denominator

So dy/dx < 0 for all x except 3

*correction to previous line: except -3*
Eric Nicholas K
Eric Nicholas K
4 months ago
I will pen this down at a later time when I am free and if no one has written them yet
4 months ago
It is ok! I understand it now :D Thank u for the quick response!

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Arnold K H Tan
Arnold K H Tan's answer
880 answers (A Helpful Person)
Alternate method:
For a decreasing function, show dy/dx is always negative for all relevant values of x.
3 months ago
Ok thank u! :)