Question

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Answer 1

1) $(x+3y)(3y-x)=$

$=(3y+x)(3y-x)=[Formula:a^2-b^2=(a-b)*(a+b)]=9y^2-x^2.$

2) $(2y+x)^2=$

$=[Formula:(a+b)^2=a^2+2ab+b^2]=4y^2+2*2yx+x^2=4y^2+4yx+x^2.$

3) $(y-2x)^2=$

$=[Formula:(a-b)^2=a^2-2ab+b^2]=y^2-2y*2x+4x^2=y^2-4yx+4x^2.$

4) $(3y-x)^2=$

$=[Formula:(a-b)^2=a^2-2ab+b^2]=9y^2-2*3xy+x^2=9y^2-6xy+x^2.$