(x+6y)(6y-x) = 6ху - х^2 + 36у^2 - 6ху = 36у^2 - х^2.
2a(4a+3)-(3a+1)^2 = 8а^2 + 6а - (9а^2 + 6а + 1) = 8а^2 + 6а - 9а^2 - 6а - 1 =
-а^2 - 1.
(x+6y)(6y-x) = 6ху - х^2 + 36у^2 - 6ху = 36у^2 - х^2.
2a(4a+3)-(3a+1)^2 = 8а^2 + 6а - (9а^2 + 6а + 1) = 8а^2 + 6а - 9а^2 - 6а - 1 =
-а^2 - 1.