1) a1=1 n=50 a50=20
S(50)=((a1+a50)/2)*50=((1+20)/2)*50=(21/2)*50=21*25
S(50)=525
2) S(100)=((1+200)/2)*100=(201/2)*100=201*50
S(100)=10050
вроде бы не ошибаюсь.
-x-y=3
x^2+y^2=5
x=-y-3
y^2+6y+9+y^2-5=0
2y^2+6Y+4=0
y&2+3y+2=0
y1=-1
x=-2
y2=-2
x=-1
(16 a^8)/a^4 = 16 a^8/a^4 = 16 a^(8-4) = 16 a^4