-
Finished your HSC? Check out our University Discussion, Non-School forums or help out next year's HSC students! -
YOU can help the next generation of students in the community! Share your trial papers and notes on our Notes & Resources page
help needed with following question sigma notation question, thanks (1 Viewer)
- Thread starter shmitler
- Start date
Split it into two separate sums.
So sum of n=1 to 20 for (3^n) + sum of n=1 to 20 for (2n-1)
Then apply the geometric sum formula for the sum of n=1 to 20 for (3^n)
i.e. 3 + 9 + 27 + .... + = a(r^n-1)/(r-1) = 3*(3^20-1)/(3-1)
Then apply arithmetic series formula for sum of n=1 to 20 for (2n-1)
i.e. 1 + 3 + 5 +....+ 39 = n/2(a+L) = 20/2(1+39)
Then add them together
So sum of n=1 to 20 for (3^n) + sum of n=1 to 20 for (2n-1)
Then apply the geometric sum formula for the sum of n=1 to 20 for (3^n)
i.e. 3 + 9 + 27 + .... + = a(r^n-1)/(r-1) = 3*(3^20-1)/(3-1)
Then apply arithmetic series formula for sum of n=1 to 20 for (2n-1)
i.e. 1 + 3 + 5 +....+ 39 = n/2(a+L) = 20/2(1+39)
Then add them together