10-х(5-(6+х))=х(х+3)-4х

10 - x( 5 - 6 - x) = x^2 + 3x - 4x 10 - x(-1 - x) = x^2 - x 10 + x + x^2 - x^2 + x = 0 2x = - 10 x= - 10/2 x = - 5