Posted by Ellie on Sunday, October 25, 2009 at 8:45pm.
Write the arithmetic sequence 21,13,5,3... in the standard form:
a_n=
a_n=a_1+(n1)dso a_n=21+(n1)8
*a_n=1688n
why isnt this right?

math  Quidditch, Sunday, October 25, 2009 at 9:00pm
You are close. You have an error:
Your step:
a_n = 21 + (n  1)  8
should be:
a_n = 21 + (n  1) * (8)

math  Ellie, Sunday, October 25, 2009 at 9:03pm
oh yeah sorry i wrote that wrong i put 1688n but it still said my answer was wrong

math  Quidditch, Sunday, October 25, 2009 at 9:15pm
a_n = 21 + (n1)*(8)
Expand that using the distributive law.
The first term, 21, is not multiplied by 8. Only the terms in parenthesis are multiplied by 8.

math  Ellie, Sunday, October 25, 2009 at 9:54pm
i figured out what i was doing thank you so much!

math  Quidditch, Sunday, October 25, 2009 at 10:03pm
You're very welcome.

math  Edward, Sunday, November 30, 2014 at 12:17am
arithmetic sequence
b_n=(2)^(n1)
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