3a (2a+7) - (2a+1) (3a-4)

3m (1-6m) - (2m-1) (2m+1)

5 (a-b) + (a+b) (a-b) - a^2

3a (2a+7) - (2a+1) (3a-4) = 6 а^2 + 21 а-6 а^2 + 8 а-3 а+4=26 а+4

3m (1-6m) - (2m-1) (2m+1) = 3m-18m^2 - 4m^2 - 2m+2m+1=-22m^2 + 3m+1

5 (a-b) + (a+b) (a-b) - a^2=5a-5b+a^2 - b^2 - a^2 = 5a-5b-b^2