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#### sweatingbear

##### Member

- May 3, 2013

- 91

\(\displaystyle bca^2 + bcd^2 + adb^2 +adc^2\),

which undeniably is a non-trivial one. It turns out that the expression can be factored into \(\displaystyle (ab + cd)(ac + bd)\). I have absolutely no idea what strategy to employ in non-trivial cases such as these (although I did attempt factoring by grouping, however to no real avail). Forum, got any clues/suggestions/tips? Anything helps!