Sn=b1(1-q^n) / (1-q)
Найдем b1.
b3=b1*q^2, отсюда b1=b3/q^2, т.е. b1=1/4 : (-1/2)^2=1/4 : 1/4 = 1
S3=1(1-(-1/2)^3) / (1+1/2)=(1+1/8) / 3/2 = 9/8 : 3/2 = 9/8 * 2/3 = 3/4
Ответ: S3=3/4.
F'(x) = 2cos(x)+4√3sin(x) ;
f"(π/3) = 2*1/2+4*√3*√3/2 = 1+(4*3)/2 = 1+6 = 7.
ответ: 7.