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Sorry about the title, if possible please change it
1. Find the sum of the following convergent series
[tex]\sum_{j=0}^{\infty}(-1)^{j}(2/3)^{j}[/tex]
2. [tex]\sum_{j=0}^{\infty}c^{j} = 1/(1-c) if |c| < 1[/tex]
= 1 - (2/3 + (2/3)^{3} + ... ) + ((2/3)^{2} + (2/3)^{4} + ...) [/tex]
Using the geometric series,
[tex]\sum_{j=0}^{\infty}(2/3)^{j} = 1 + (2/3) + (2/3)^{2} + ... = 1/(1-(2/3)) = 3
= 1 + (2/3 + (2/3)^{3} + ...) + ((2/3)^{2} + (2/3)^{4} + ...) [/tex]
[tex](2/3)^{2} + (2/3)^{4} + ...) = 2 - (2/3 + (2/3)^{3} + ...) [/tex]
substituting into the original problem:
[tex]\sum_{j=0}^{\infty}(-1)^{j}(2/3)^{j} = 1 - (2/3 + (2/3)^{3} + ... ) + (2 - (2/3 + (2/3)^{3} + ...)
= 3 - 2(2/3 + (2/3)^{3} + ... ) [/tex]
Now i don't know what to do, would like some help, thanks!
1. Find the sum of the following convergent series
[tex]\sum_{j=0}^{\infty}(-1)^{j}(2/3)^{j}[/tex]
2. [tex]\sum_{j=0}^{\infty}c^{j} = 1/(1-c) if |c| < 1[/tex]
The Attempt at a Solution
[tex]\sum_{j=0}^{\infty}(-1)^{j}(2/3)^{j} = 1 - 2/3 + (2/3)^{2} + ...= 1 - (2/3 + (2/3)^{3} + ... ) + ((2/3)^{2} + (2/3)^{4} + ...) [/tex]
Using the geometric series,
[tex]\sum_{j=0}^{\infty}(2/3)^{j} = 1 + (2/3) + (2/3)^{2} + ... = 1/(1-(2/3)) = 3
= 1 + (2/3 + (2/3)^{3} + ...) + ((2/3)^{2} + (2/3)^{4} + ...) [/tex]
[tex](2/3)^{2} + (2/3)^{4} + ...) = 2 - (2/3 + (2/3)^{3} + ...) [/tex]
substituting into the original problem:
[tex]\sum_{j=0}^{\infty}(-1)^{j}(2/3)^{j} = 1 - (2/3 + (2/3)^{3} + ... ) + (2 - (2/3 + (2/3)^{3} + ...)
= 3 - 2(2/3 + (2/3)^{3} + ... ) [/tex]
Now i don't know what to do, would like some help, thanks!
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