Question

S2=1 supra 1*4+1 supra 4*7+1 supra 7*10+...+1 supra 82*85
VA ROG REPEDE!!!!!!

Answer 1

1/1x4=(1-1/4)/3
1/4x7=(1/4 - 1/7)/3
1/7x10=(1/7 - 1/10)/3
........................

1/79x82=(1/79 - 1/82)/3
1/82x845=(1/82 - 1/85)/3, le adunam si dam factor comun pe 1/3
S2=(1/4 - 1/7+1/7 - 1/10+...............+1/79 - 182+1/82 - 1/85)/3
S2=(1/4 - 1/85)/3=27/340