Question

1+4+7+......+100 calculati

Answer 1

100=1+(n-1)x3
100=1+3n-3
3n=102
n=34 termeni

suma:
34=2+33x3/2x34
34=101x17
34=1717 numere

Answer 2

100 = 1+ (n-1) x 3 
100 = 1 + 3n - 3
3n = 100 - 1 + 3 
3n = 102 
n = 34 de termeni se afla in suma

S.34 = 2+33x3 / 2  x 34 
S.34 = 2+99 /2   x 34
S.34 = 101 / 2  x 34
S.34 = 101 x 17 
S.34 = 1717 suma