Question

Fie sirul 1;4;7;10
afla suma primilor 100 de termeni

Answer 1

a1=1
a2=1+3=4
a3=a2+3=1+2*3=7
a4=a3+3=1+3*3=10
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a100=1+99*3
le  adui
a1+...+a100=1+(1+3)+(1+2*3)=...+(1+99*3)=(1++1+,,,+1)(de  100 de  ori)+
(1*3+2*3+..+99*3)=100+3*(1+2+...+99)
1+2+...+99=99*100/2=4950  o  suma  Gauss
Suma  finala=100+4950=5050