19. докажите тождество (6х-8у+7)*(6х+8у-7)+(8у-7)^2=36х^2 (9k+11+2m+n)*(9k-2m+11-n)-9k(9k+22)+4m(m+n)=121-n^2 ​

Объяснение:

(6х-8у+7)*(6х+8у-7)+(8у-7)^2=

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

=(6x)^2-(8y-7)^2+(8y-7)^2=(6x)^2=36x^2    доказано

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

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

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

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

=11^2-n^2=121-n^2                  доказано