jenny06181 jenny06181

27-04-2017
Mathematics

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Given the arithmetic series 30+25+20+15+10... Find the sum of the first n terms when n=42

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zebsi0n zebsi0n

27-04-2017

[tex]S(n) = \frac{n}{2}(2a(1)+(n-1)d) [/tex]
What is a(1)? 30.
What is d? Seems to be -5.
What is n? 42
So...
[tex]S(42) = 21((2*30)+(41*-5))[/tex]
[tex]S(42) = 21(60-205)[/tex]
[tex]S(42)= -3045[/tex]

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