y'*sin(x) = y*логарифм(y)
Cos 2.3, cos 5, cos 1, cos 7.
Tg31П/6=tg(31pi/6-5pi)=tgpi/6=1/sqrt(3)
(2 TgП/6 - TgП/3): cosП/6=(2sqrt(3)-sqrt(3)/3)*2/sqrt(3)=4-2/3=10/3
Ctg13П/4=ctg(13pi/4-3pi)=ctgpi/4=1
cos19П/3=cos(19pi/3-6pi)=cospi/3=1/2
Аn=a1+d(n-1)
12=68+(-4)*n+(-4)
12=64-4n
-52=-4n
n=13
a13=12
S(n)=((a1+an)/2)*n
S(13)=((68+12)/2)*13=40*13=520