# Consider your summer job…..did you ever get a raise? Suppose you get paid $100.00 per week, with a $5 raise each week. How much will you have at the

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Slide 2 Slide 3 Consider your summer job..did you ever get a raise? Suppose you get paid $100.00 per week, with a $5 raise each week. How much will you have at the end of the summer (4 weeks)? 100, 105, 110, 115 Slide 4 To find a total, create an arithmetic series With small amounts, it is easy to calculate the totals manually. However, as we study more complex relationships, a more efficient method is needed.. 100 + 105 + 110 + 115 = 430 Slide 5 Watch this + S = 100 + 105 + 110 + 115 S = 115 + 110 + 105 + 100 2S = 215 + 215 + 215 + 215 2S = 215(4) 2S = 860 S = 430 Slide 6 There is an even quicker way.. Find the mean of the first and last term (100 + 115) = 107.5 2 Multiply by the number of terms 107.5 X 4 = 430 HOW? Slide 7 Find the sum of 10,15,20,25,30 10 + 15 + 20 + 25 + 30 = 100 30 + 10 2 =20 20 X 5 = 100 20 + 20 + 20 + 20 + 20 Consider the numbers forming a bar graph. 20 Slide 8 If we extend this approach to the general case, we can then generate a formula that will allow us to find the sum of a series of any length! Slide 9 Sum of an Arithmetic Series S n = (mean of first and last term) ( n ) 2 (number of terms) X S n = (a + t n ) X Slide 10 Since t n = a + (n 1)d, - make the substitution ( n ) 2 S n = (a + t n ) X ( n ) 2 S n = [a + a + (n 1)d] X Collect the as and multiply by n Slide 11 S n = n [2a + (n 1)d] 2 n = term number a = first term d = common difference Slide 12 Determine the sum: 1) 2 + 4 + 6 + 8 + 10 =30 S n = n [2a + (n 1)d] 2 n = 5 a = 2 d = 2 Slide 13 S n = n [2a + (n 1)d] 2 n = 5, a = 2, d = 2 S 5 = 5 [2(2) + (5 1)2] 2 = 5 [4 + 8] 2 = 5 [12] 2 = 30 Slide 14 Find the sum: -4, -10, -16, -94 S n = n [2a + (n 1)d] 2 n = ? a = -4 d = -6 Use the term formula to find n Slide 15 t n = -94 a = -4 d = -6 Since t n = a + (n 1)d, -94 = -4 + (n 1)(-6) -94 = -4 6n + 6 -96 = - 6n n = 16 Slide 16 Find the sum: -4, -10, -16, -94 S n = n [2a + (n 1)d] 2 n = 16 a = -4 d = -6 Go back . Slide 17 S n = n [2a + (n 1)d] 2 n = 16, a = -4, d = -6 S 16 = 16 [2(-4) + (16 1)(-6)] 2 = 16 [(-8) + (-90)] 2 = 8 [-98] = -784 Slide 18 The sum of the first 4 terms of an arithmetic series is 8 and the sum of the first 5 terms is 85. Determine the first term and the common difference. Slide 19 ____ + ____ + ____ + ____ = -8 Let the first term be a, let the common difference be d ____ + ____ + ____ + ____ + ____ = 85 a a + da + 2da + 3d aa + da + 2d a + 3da + 4d Generate a linear system with 2 equations and 2 unknowns Slide 20 ____ + ____ + ____ + ____ = -8 a + a + d + a + 2d + a + 3d = -8 a + a + d + a + 2d + a + 3d + a + 4d = 85 ____ + ____ + ____ + ____ + ____ = 85 a a + da + 2da + 3d aa + da + 2d a + 3da + 4d 4a + 6d = -8 5a + 10d = 85 Slide 21 - X 5 X 4 4a + 6d = -8 5a + 10d = 85 20a + 30d = -40 20a + 40d = 340 - 10d = -380 d = 38 4a + 6(38) = -8 4a + 228 = -8 a = -59 Substitute Slide 22 Page 469 [1-3] a,c 6,11,13, 15,19, 23 quiz wed test friday Slide 23 Page 56 [1,3,5]a,c 6a, 9a,c,e 10,13,17 19,20,22*

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