приложи картинку с заданием
<span>cos17cos73=0.5(cos90+cos56)</span>
<span><span>sin13cos21=0.5(sin34-sin8)</span></span>
<span><span><span>cos4cos86=0.5(cos90+cos82)</span></span></span>
<span><span><span>cos90=0</span></span></span>
<span><span><span>cos56=cos(90-34)=sin34</span></span></span>
<span><span><span>cos82=cos(90-8)=sin8</span></span></span>
<span><span><span><span>cos17cos73-sin13cos21-cos4cos86=0.5(sin34-sin34+sin8-sin8)=0</span></span></span></span>
D=100-4*25=0
x=-b/2a
x=10/2=5
это первый
D=81-32=49
x1=(9-7)/2=1
x2=(9+7)/2=8
(x-1)(x-8)