Oh, I see. I thought cross multiplying was referring to what you do in order to add or subtract two fractions with different denominators. Should have just look

Oh, I see. I thought cross multiplying was referring to what you do in order to add or subtract two fractions with different denominators. Should have just looked it up. The failing here is that you don't understand why you get the right answer here. By 'you' you mean the putative student mislead by shortcuts, right? I understand perfectly well what's happening with reciprocal multiplication and why it works. ;)