1) (11а - b)^2 + (9a + 7b)(8a - 13b) = 121a^2 - 22ab + b^2 + 72a^2 - 117ab + 56ab - 91b^2 = 193a^2 - 83ab - 90b^2
2) (18x + 5y)(2x - 4y) - (6x - 3y)^2 = 36x^2 - 72xy + 10xy - 20y^2 - 36x^2 + 36xy - 9y^2 = - 29y^2 - 26xy
3) 4х(3х - 2у) - (10у - 0,4х)^2 = 12х^2 - 8ху - 100у^2 + 8ху - 0,16х^2 = 11,84х^2 - 100у^2