Question

Progresii aritmetice//1 + 4 + 7 + ... + 100 = ?​

Answer 1

Se observa ca termenii sunt intr o progresie aritmetica cu ratia=3 si a1=1

an=100

an=a1+(n-1)*r

100=1+(n-1)*3

99=3n-3

102=3n

n=102/3

=34

Suma primilor 34 de termeni

S34=(an+a1)*n/2

=(100+1)*17

=101*17

=1717