1)(x+3)^2-1=х^2+6x+9-1=x^2+6x+8;
2)49x^2-(y+8x)^2=49x^2-y^2-16x+64x^2=113x^2-y^2-16x;
3)9-(7+3a)^2=9-49-42a-9a^2=-40-42a-9a^2;
4)(a+b)^2-(b-c)^2=a^2+2ab+b^2-b^2+2bc-c^2=a^2+2ab+2bc-c^2=(a^2-c^2)+2b(a+c)=(a+c)(a-c+2b);
5)(4a-3)^2-16=16a^2-24a+9-16=16a^2-24a-7;
6)(2b-25)^2-36=4b^2-100b+625-36=4b^2-100b+589;
7)p^2-(2p+1)^2=p^2-4p^2-8p-1=-3p^2-8p-1;
8)(m+n)^2-(m-n)^2=m^2+2mn+n^2-m^2+2mn-n^2=4mn;
9)9y^2-(1+2y)^2=9y^2-1-4y-4^2=5y^2-4y-1;
10)(4-11m)^2-1=16-88m+121-1=136-88m;
11)(2x+y)^2-(x-2y)^2=4x^2+4xy+y^2-x^2+4xy-4y^2=3x^2+8xy-3y^2;
12)(4c-x)^2-(2c+3x)^2=16c^2-8cx+x^2-4c^2-12cx-9x^2=12c^2-20cx-8x^2;