По теореме Виета
x^2 + px + q = 0
x1 + x2 = - p
x1*x2 = q
x^2 - 16x + 28 = 0
x1 + x2 = 16
x1*x2 = 28
<span> (y-3)(y+5)= у^3+5y-3y-15=y^3+2y-15</span>
5 arccos 1/2+3 arcsin (-sqrt 2/2) = 5*П/3 - 3*П/4 = 11П/12