(9a-2)(9a+2) ; 25m во2 степени - (5m-7)(5m+7) ; (b+7)(b-4)+(2b-6)(2b+6)

1) (9a-2)(9a+2)=(9a)^2-2^2= 81a^2-4
2) 25m^2-(5m-7)(5m+7)=625m^2-(25m^-49)=625m^2-25m^2+49=600m^2+49
3) (b+7)(b-4)+(2b-6)(2b+6)=(b^2+3b-28)+(4b^2-36)=b^2+3b-28+4b^2-36=5b^2+3b-64