Find the missing term: $(2m + \Box)^{2} = 4m^{2} + 12mn + 9n^{2}$.

Find the missing term: $(2m + \Box)^{2} = 4m^{2} + 12mn + 9n^{2}$.
  1. $3n$
  2. $6n$
  3. $9n$
  4. $3n^{2}$

Solution

Last term $9n^{2} = (3n)^{2}$ and middle $12mn = 2(2m)(3n)$. So missing term is $3n$.

Asked in: IMO

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