Mark Thong's answer to Walking's Junior College 2 H1 Maths question.
Hmmmm I think you got the qn upside down. The qn is if x is real then prove the inequality. Not given the given the inequality, prove that x is real.
Hmm.. i think you didn't follow my reasoning and conclusion. :)
Note the double implication i used on each step, and in the end i mentioned "implying backwards".
Note the double implication i used on each step, and in the end i mentioned "implying backwards".
I mean can you start off like that and do the "double implication". Issit legit?
The question is.. Is the logic Of the proof sound And correct?
A <=> B <=> C <=> D
Hence D => A
Correct?
A <=> B <=> C <=> D
Hence D => A
Correct?
Yeap I get your logic but I just thought given the way the qn is asked, direct proofs make more sense ie, start with -(x-3)²≤0≤11(x+3)²
Instead of going by your way of "indirect" proof I suppose? I'm not sure actually, I'm not a math major :/
Instead of going by your way of "indirect" proof I suppose? I'm not sure actually, I'm not a math major :/
But in the first place, how woud you know to start with -(X-3)² ≤ 0 ≤ 11(x+3)² ?
So your "direct approach" is merely working backwards.
Neither am i a math major.. ;)
So your "direct approach" is merely working backwards.
Neither am i a math major.. ;)
I didn't get it...
Wow why can you add the equal there
What is the meaning of implying backwards
qn meaning?
A B C D there I didn't get it too...
Yeap work backwards. This is akin to finding the epsilon when doing limits problems. They begin with some rough work and then start the actual proof by working backwards from there. I mean your logic is fine, it's just the presentation seems awkward to me :/
Maybe we should stick to calculus hahaha
Maybe we should stick to calculus hahaha
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