(x-3)/(x²+3x):2/(x+3)=(x-3)/x(x+3) . (x+3)/2=(x-3)(x+3)/2x(x+3)=
=(x-3)/2x
x=5, (5-3)/2.5=2/10=1/5=0,2
Cos17cos73_cos13cos21_cos4cos86=_34
A1+3d+a1+15d=24 => 2a1+18d=24
a1+8d+a1+19d=-12 => 2a1+27d=-12 =>
![\left \{ {{2a1+18d=24} \atop {2a1+27d=-12}} \right.](https://tex.z-dn.net/?f=+%5Cleft+%5C%7B+%7B%7B2a1%2B18d%3D24%7D+%5Catop+%7B2a1%2B27d%3D-12%7D%7D+%5Cright.+)
, вычитаем:
2a1+18d-2a1-27d=24+12, -9d=36 => d=-4;
2a1+18d=24 , 2a1+18*(-4)=24 , 2a1-72=24 => 2a1=96, a1=48.