B1=3/5 q=3 sn=b1*(qⁿ-1)/(q-1)
s7=3/5*[(3⁷-1)/(3-1)]=(3/5)*2186/2=655.8
Y(1)=4-9+13=8
y(2)=4*8-9*4+13=32-36+13=9
y(3)=4*27-9*9+13=108-81+13=40
Ответ: 8.
6*3-√17(6*3+1)=18-√17*(19)=18-19√17
Cos(2x) - cos(3x) = 2*((sin(2x+3x)/2)*(sin(3x-2x)/2) = 2*(sin(5x)/2)*sin(x/2))