Welcome Activity 1. Find the sum of the following sequence: 2 + 4 + 6 + 8 + 10 2. Find the number of terms (n) in the following sequence: 5, 9, 13, 17, … 81, 85
HW Key
Summation Notation & Arithmetic Series Unit 1 Chapter 11 Summation Notation & Arithmetic Series
Objectives Students will be able to find the partial sum of an arithmetic series. HW: p. 780: 30, 32, 38, 50, 60
A series is formed when the terms of a sequence are added. In general, the sum of n terms in a finite series is written u1 + u2 + u3 + . . . + un = Sn The sum of an infinite series is written: u1 + u2 + u3 + . . . = S∞
This sum can be expressed using a shorthand notation: u1 + u2 + u3 + . . . + un = Sn = u1 + u2 + u3 + . . . = S∞ = Please note that i in this context does not refer to imaginary numbers.
Ex 1: Find the sum of the series.
Ex 2: Write the series in summation notation. 3 + 5 + 7 + 9 + 11 + 13
When the famous mathematician Karl Friedrich Gauss (1777-1855) was nine years old, his teacher asked the class to find the sum of the numbers from 1 to 100. Historical accounts indicate the teacher was hoping to take a break from his students and expected the students to add the terms one by one.
1 + 2 + 3 + . . . + 98 + 99 + 100 = S100 100 + 99 + 98 + . . . + 3 + 2 + 1 = S100 101 + 101 + 101 + . . . + 101 + 101 + 101 = 2 (S100)
Gauss’ creative thinking can be used to derive the explicit formula for the sum of an arithmetic series: u1 + u2 + u3 + . . . + u n - 2 + u n - 1 + u n = Sn u n + u n - 1 + u n - 2 + . . . + u3 + u2 + u1 = Sn (u1 + u n ) · n = 2 (Sn)
Explicit Formula for the sum of an arithmetic series: where n is the number of terms, u1 is the first term, and un is the last term.
Ex 3: Find the sum of the first 10 terms given: a3 = 5 and a4 = 8.
Ex 4: Find the sum of the first 50 multiples of 6.
Ex 5: Find a1 and d given S20 = 1090 and a20 = 102
Ex 6: Find the sum of the arithmetic series: 89 + 84 + 79 + 74 + . . . + 9 + 4
Ex 7: Evaluate the sum: