1) Верный ответ под буквой Г .

[tex]\displaystyle\bf\\1)\\\\(2x-7)^{2} -49=(2x)^{2} -2\cdot 2x\cdot 7+7^{2} -49=\\\\=4x^{2} -28x+49-49=4x^{2} -28x\\\\2)\\\\16+(3m+4)(3m-4)=16+(3m)^{2} -4^{2} =\\\\=16+9m^{2} -16=9m^{2} \\\\3)\\\\(6y+1)^{2} +(5-6y)(5+6y)=(6y)^{2} +2\cdot 6y\cdot 1+1^{2} +5^{2} -(6y)^{2} =\\\\=36y^{2} +12y+1+25-36y^{2} =12y+26[/tex]