InterviewSolution
Saved Bookmarks
| 1. |
`sum_(r=1)^(n)(3^(r)-2^(r))=.............` |
|
Answer» Correct Answer - A::B::C `sum_(r=1)^(n)(3^(r)-2^(r))=sum_(r=1)^(n)3^(r)-sum_(r=1)^(n)2r` `=(3+3^(2)+3^(3)+.........+3^(n))=(3(3^(n)-1))/(3-1)=(2(2^(n)-1))/(2-1)` `=(3^(n+1))/(2)-(3)/(2)-2^(n+1)+2(2+2^(2)+2^(3)+..........+2^(n))` `=(3^(n+1))/(2)-2^(n+1)+(1)/(2)=(3^(n+1)-2^(n+2)+1)/(2)` |
|