Problem :
Find an explicit formula for the following sequence: 1, 3, 5, 7, 9,....
an = 2n - 1
Problem :
Find three explicit formulas for the following sequence: -1, 1, -1, 1, -1, 1,… (Hint: Use trigonometric functions, too).
an = (- 1)n;
an = sin(
+ nΠ);
an = cos(nΠ).
Problem :
What is the 11th term of the sequence an = 2n - 6?
a11 = 2(11) - 6 = 16.
Problem :
Calculate 
(4i - 5).
(4i - 5) = - 1 + 3 + 7 + 11 + 15 + 19 = 54.
Problem :
Calculate 
5(k + 2).
5(k + 2) = 5(k + 2) = 5[6 + 7 + 8 + 9] = 150.
Problem :
Let an = 4n2. What is the sum of the first five terms of a?
(4i2) = 4i2 = 4[1 + 4 + 9 + 16 + 25] = 220.
