<span>2x+6+x^2+3x
x^2+5x+6=0</span>
D=b^2-4ac
D=25-4*1*6
D=1
x=-b(+-)D/2a
x1=(-5+1)/2=-2
x2=(-5-1)/2=-3
x(x+2)(x+3)
Cos(x-5/(pi2))=cos(х) cos(5/(pi2))+sin(х) sin(5/(pi2))= sinx
<span>если у вас написано 5pi/2 то cos(5pi/2)=0 </span>
<span>sin(5pi/2)=1 </span>
<span>cos(2x)=1-2sin^2(x) </span>
<span>1-2sin^2(x)-sinx-1=0 </span>
<span>sinx(2sinx+1)=0 </span>
<span>sinx=0, </span>
<span>x= n pi </span>
<span>и </span>
<span>sinх= -0.5, </span>
<span>x= -pi/6+2pi n </span>
<span>x= -5pi/ 6+2pi n </span>