Big Ideas Math Algebra 2, 2014
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Big Ideas Math Algebra 2, 2014 View details
2. Analyzing Arithmetic Sequences and Series
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Exercise 4 Page 417

Practice makes perfect
a We are asked to find the sum of the following arithmetic sequence.
1, 4, 7, 10, ..., 301 For this sequence, the first sequence is a_1= 1, the common difference is d=4-1= 3, and the last term is a_n= 301. First, let's find the number of terms in the given sequence. We will use the formula for the explicit rule of arithmetic sequences. a_n= a_1+(n-1) dNow, we will substitute values into the formula and solve if for n.
a_n= a_1+(n-1) d
301= 1+(n-1)( 3)
â–Ľ
Solve for n
301=1+3n-3
301=3n-2
303=3n
101=n
n=101
Next, we will calculate the sum of the given sequence. 1+4+7+...+301 To do this, we will use the formula for finding the sum of an arithmetic series for n=101. S_()darkorangen=n(a_1+a_()darkorangen)/2 ⇓ S_()darkorange101=101(a_1+a_()darkorange101)/2 Finally, we will substitute 1 for a_1 and 301 for a_(101), and then find the sum.
S_(101)=101( a_1+ a_(101))/2
S_(101)=101( 1+ 301)/2
â–Ľ
Simplify right-hand side
S_(101)=101(302)/2
S_(101)=30 502/2
S_(101)=15 251
This tells us that the sum of the given arithmetic sequence is 15 251.
b We are asked to find the sum of the following arithmetic sequence.
1, 2, 3, 4, ..., 1000 For this sequence, the first sequence is a_1= 1, the common difference is d=2-1= 1, and the last term is a_n= 1000. First, let's find the number of terms in the given sequence. We will use the formula for the explicit rule of arithmetic sequences. a_n= a_1+(n-1) dNow, we will substitute values into the formula and solve if for n.
a_n= a_1+(n-1) d
1000= 1+(n-1) 1
â–Ľ
Solve for n
1000=1+n-1
1000=n
n=1000
Next, we will calculate the sum of the given sequence. 1+2+3+...+1000 To do this, we will use the formula for finding the sum of an arithmetic series for n=1000. S_()darkorangen=n(a_1+a_()darkorangen)/2 ⇓ S_()darkorange1000=1000(a_1+a_()darkorange1000)/2 Finally, we will substitute 1 for a_1 and 1000 for a_(1000), and then find the sum.
S_(1000)=1000( a_1+ a_(1000))/2
S_(1000)=1000( 1+ 1000)/2
â–Ľ
Simplify right-hand side
S_(1000)=1000(1001)/2
S_(1000)=1 001 000/2
S_(1000)=500 500
This tells us that the sum of the given arithmetic sequence is 500 500.
c We are asked to find the sum of the following arithmetic sequence.
2, 4, 6, 8, ..., 800 For this sequence, the first sequence is a_1= 2, the common difference is d=4-2= 2, and the last term is a_n= 800. First, let's find the number of terms in the given sequence. We will use the formula for the explicit rule of arithmetic sequences. a_n= a_1+(n-1) dNow, we will substitute values into the formula and solve if for n.
a_n= a_1+(n-1) d
800= 2+(n-1) 2
â–Ľ
Solve for n
800=2+2n-2
800=2n
400=n
n=400
Next, we will calculate the sum of the given sequence. 2+4+6+...+800 To do this, we will use the formula for finding the sum of an arithmetic series for n=400. S_()darkorangen=n(a_1+a_()darkorangen)/2 ⇓ S_()darkorange400=400(a_1+a_()darkorange400)/2 Finally, we will substitute 2 for a_1 and 800 for a_(400), and then find the sum.
S_(400)=400( a_1+ a_(400))/2
S_(400)=400( 2+ 800)/2
â–Ľ
Simplify right-hand side
S_(400)=400(802)/2
S_(400)=302 800/2
S_(400)=160 400
This tells us that the sum of the given arithmetic sequence is 160 400.