3.5 х (х+2/1.4) = 14

3,5 х (х + 2/1,4) = 14;

3,5x (x + 20/14) = 14;

3,5x^2 + 70x/14 = 14;

3,5x^2 + 5x = 14;

3,5x^2 + 5x - 14 = 0;

D = 25 - 4 * 3,5 * (-14) = 25 + 196 = 221;

x = (-5 +- sqrt221)/7;

х1 = (-5 - sqrt221)/7;

x2 = (-5 + sqrt221)/7.

Ответ:  (-5 - sqrt221)/7, (-5 + sqrt221)/7.