помогите плиз, даю 20 балов

1) (a-m+7)(a+m-7)-a²=(a-(m-7))(a+(m-7))-a²=a²-(m-7)²-a²=-(m-7)².

2) (3x+5-y)(3x+5+y)+y²=((3x+5)-y)((3x+5)+y)+y²=(3x+5)²-y²+y²=(3x+5)².

3) (6x-8y+7)(6x+8y-7)+(8y-7)²=(6x-(8y-7))(6x+(8y-7))+(8y-7)²=

=(6x)²-(8y-7)²+(8y-7)²=36x².

4) (9k+11+2m+n)(9k-2m+11-n)-9k*(9k+22)+4m*(m+n)=

= (9k+11+(2m+n)) (9k+11-(2m+n))-9k*(9k+22)+4m*(m+n)=

=(9k+11)²-(2m+n)²-9k*(9k+22)+4m*(m+n)=

=81k²+198k+121-4m²-4mn-n²-81k²-198k+4m²+4mn=121-n².