9. Explain the process of cross-multiplication.
2 answers
http://www.aaamath.com/rat-prop-crossx.htm
I object!!!! I would never teach cross-multiplication. While it appears to work often, and in the above link as an example, here is where it gets students into trouble...
(x+3)/2=(5/7)+3/1
So many students apply "cross multiplication and get results such as this.
a. x*7=5*2+3 or
b. 7*1(x+3)=13
or many other variants. If you forget about "cross-multiplying", you will never have this issue.
It is so much easier to just take operations wherein you multiply/divide both sides of the equation by the same factors.
example: 7*2(x+3)/2=7*2((5/7)+3/1)
or 7(x+3)=10+14*3/1
which is quite different from the earlier results.
(x+3)/2=(5/7)+3/1
So many students apply "cross multiplication and get results such as this.
a. x*7=5*2+3 or
b. 7*1(x+3)=13
or many other variants. If you forget about "cross-multiplying", you will never have this issue.
It is so much easier to just take operations wherein you multiply/divide both sides of the equation by the same factors.
example: 7*2(x+3)/2=7*2((5/7)+3/1)
or 7(x+3)=10+14*3/1
which is quite different from the earlier results.
1 answer