Question 864063
Use the FOIL method,
{{{(5m-2n)^2=(5m-2n)(5m-2n)}}}
First:{{{5m(5m)=25m^2}}}
Outer:{{{5m(-2n)=-10mn}}}
Inner:{{{-2n(5m)=-10mn}}}
Last :{{{-2n(-2n)=4n^2}}}
Add it up,
{{{(5m-2n)^2=25m^2-10mn-10mn+4n^2}}}
{{{highlight((5m-2n)^2=25m^2-20mn+4n^2)}}}