10 га = 70*10 = 700 т
100 га = 70*100 = 7000 т
m га = 70m т
16000 = 70*16000 = 1120000 т
An = A1 + (n - 1)D;
A1 = An - (n - 1)D;
A1 = 38 - (15 - 1)*3 = 38 - 14*3 = 38 - 42 = -4;
Sn = n*(2A1 + D(n-1))/2
S10 = 10*(2*(-4) + 3(10-1))/2 = 10*(-8 + 27)/2 = 5*19 = 95;
15-4 1/8=10 7/8
3 14/15-2 3/5=1 1/3
7/8*1 1/3=14 1/2
12! · 6! / 16! =
= 12! · 6! / 12! ·13·14·15·16 =
= 6! / 13·14·15·16 =
= 1·2·3·4·5·6/13·14·15·16 =
= 3/ 13·14 =
= 3/182