Our math teacher said that cross multiplication method is not a logical method to solve in!!! even if the answer is right!!!

so is he right?

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- Nov 7th 2009, 03:59 AMlebanonIs it logical???
Our math teacher said that cross multiplication method is not a logical method to solve in!!! even if the answer is right!!!

so is he right? - Nov 7th 2009, 02:43 PMMedia_Man
If you are referring to the property in algebra that $\displaystyle \frac{a}{b}=\frac{c}{d}$ implies $\displaystyle ad=bc$ provided of course b,d are nonzero... then yes, this is a valid and completely sound property of real numbers.

Perhaps what your professor means by "illogical" is that cross-multiplication is not a fundamental property or operation in algebra. The correct and logical step is to multiply both sides of the equation by $\displaystyle bd$. The term "cross multiply" is not so much a mathematical tool as it is a teaching tool, to help young (particularly math-hating) students remember how to proceed when faced with this type of problem. - Nov 8th 2009, 08:10 PMlebanon
Thanks very much, because I was really confused