(5x+y)^2​​ −(x−5y)^2
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(5x+y)^2​​ −(x−5y)^2==(5x+y(x-5y))*(6x+y+x-5y)==(5x+y-x+5y)*(6x-4y)==(4x+5y)*2(3x-2y)==2(2x+3y)*2(3x-2y)==4(2x+3y)*(3x-2y).