a1 = 30; d = -2 аn = 30 -2*(n-1) a14 = 4 S14 = (a1+a14)*7 = 34*7 = 238
=> a1=30; a2=28; a3=26
d=a2-a1=28-30=-2
s14=(a1+a14)14/2
a14=a1+d*13=30+(-2)*13=4
s14=((30+4)14)/2=476/2=238
a1 = 30; d = -2
аn = 30 -2*(n-1)
a14 = 4
S14 = (a1+a14)*7 = 34*7 = 238
=> a1=30; a2=28; a3=26
d=a2-a1=28-30=-2
s14=(a1+a14)14/2
a14=a1+d*13=30+(-2)*13=4
s14=((30+4)14)/2=476/2=238