(2a-1)^2=4a^2-4a+1
(x+3y)^2=x^2+6xy+9y^2
(7-x)(7+x)=49-x^2
3x^2-6xy+3y^2=x^2-2xy+y^2=3(x-y)^2
5x^2-5y^2=x^2-Y^2=(x-y)(x+y)
(x+5)^2-5x(2-x)=x^2+10x+25-10x+5x^2=6x^2+25
(2a-1)^2=4a^2-4a+1
(x+3y)^2=x^2+6xy+9y^2
(7-x)(7+x)=49-x^2
3x^2-6xy+3y^2=x^2-2xy+y^2=3(x-y)^2
5x^2-5y^2=x^2-Y^2=(x-y)(x+y)
(x+5)^2-5x(2-x)=x^2+10x+25-10x+5x^2=6x^2+25