[tex]\displaystyle\bf\\1)\\\\c^{2} - d^{2} -c-d=(c^{2} -d^{2} )-(c+d)=(c+d)(c-d)-(c+d)=\\\\=(c+d)(c-d-1)\\\\2)\\\\a^{2} -10a+25-ab+5b=(a^{2} -10a+25)-(ab-5b)=\\\\=(a-5)^{2} -b\cdot(a-5)=(a-5)(a-5-b)\\\\3)\\\\b^{2} (a+1)-a^{2} (b+1)=ab^{2} +b^{2} -a^{2} b-a^{2} =\\\\=(ab^{2} -a^{2} b)+(b^{2} -a^{2} )=ab\cdot(b-a)+(b-a)(b+a)=\\\\=(b-a)(ab+b+a)[/tex]