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secondary 2 | Maths
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Hania
Hania

secondary 2 chevron_right Maths chevron_right Singapore

Why does the plus become a minus sign??

Date Posted: 4 years ago
Views: 273
Eric Nicholas K
Eric Nicholas K
4 years ago
Because of what we call “magic”.
Hania
Hania
4 years ago
Huh
Eric Nicholas K
Eric Nicholas K
4 years ago
You can just change the + sign in the question to become a - sign.

I can’t believe that a typo could be made in a book when the expression is relatively short.
Hania
Hania
4 years ago
So the solution is wrong?
Eric Nicholas K
Eric Nicholas K
4 years ago
Or rather, the solution is correct and the question is incorrect.

Because there is a mismatch between the question and the start of the solution (a copying error).
Hania
Hania
4 years ago
So Would the symbols be the same and not change in the answer?
Eric Nicholas K
Eric Nicholas K
4 years ago
I myself have made such “transcript errors” before, where I copied down the question wrongly but answered the “incorrect” question correctly.

Yesterday my student just made one similar mistake by missing out a term from an expression.
Eric Nicholas K
Eric Nicholas K
4 years ago
In such cases, the signages should remain.

So,

12x^2 + 24x
= 12x (x + 2)

where the common terms are 12 and x.

12x^2 - 24x
= 12x (x - 2)

where the common terms are 12 and x.

We do not extract out any negative sign at all, so the signages should not change at all.
Hania
Hania
4 years ago
Thank you so much
Eric Nicholas K
Eric Nicholas K
4 years ago
In this case, however, the signage will change.

-12x^2 - 24x
= -12x (x + 2)

Observe that a - sign has been extracted out, so the signages of the expression must change.
Hania
Hania
4 years ago
Ohhh ok thank you

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