1) (2а+1)^2=(2a+1)(2a+1)=4a^2+4a+1
2) (c-4p)^2=(c-4p)(c-4p)=c^2-8cp+16p^2
3) (b+7)(b-7)=b^2-49
4) (2x-1)(2x+1)-2x(3x-5)=4x^2-1+(-6x^2+10)=-2x+10x-1
5) 6y(y+5)-(2y-3)^2=6y^2+30y+(-4y^2+12y-9)=2y^2+42-9
6) 4(x-2y)^2+16xy=4x^2-16xy+16y^2+16xy=4x^2+16y^2