Answer
$25x^{2}+20xy+4y^{2}$
Work Step by Step
$(5x+2y)^{2}=(5x+2y)(5x+2y)=5x(5x+2y)+2y(5x+2y)=(5x)(5x)+(5x)(2y)+(2y)(5x)+(2y)(2y)=25x^{2}+10xy+10xy+4y^{2}=25x^{2}+20xy+4y^{2}$
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