How do you factor by grouping $mr + ns - nr - ms$ ?

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Answer 1 · 2018-03-15T00:09:37

I tried this:

Collect $r$ from the first and third term and $-s$ from the second and fourth:

$mr+ns-nr-ms=r(m-n)-s(m-n)=$

now collect $m-n$ :

$=(m-n)(r-s)$

How do you factor by grouping mr + ns - nr - msmr + ns - nr - ms?