Show that for any z C an Z not equal to 1 one has

1 + z +...+z^n = (1-z^(n+1))/(1-z)

and use it to show that

1 + from k=1 to n of cos(k ) = 1/2 + (sin((2n+1) /2))/(2sin( /2))

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- Jan 28th 2010, 01:52 PMLCopper2010more complex variable help
Show that for any z C an Z not equal to 1 one has

1 + z +...+z^n = (1-z^(n+1))/(1-z)

and use it to show that

1 + from k=1 to n of cos(k ) = 1/2 + (sin((2n+1) /2))/(2sin( /2)) - Jan 28th 2010, 06:34 PMTheEmptySet