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secondary 2 | Maths
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Why does the plus become a minus sign??
I can’t believe that a typo could be made in a book when the expression is relatively short.
Because there is a mismatch between the question and the start of the solution (a copying error).
Yesterday my student just made one similar mistake by missing out a term from an expression.
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.
-12x^2 - 24x
= -12x (x + 2)
Observe that a - sign has been extracted out, so the signages of the expression must change.
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