math
posted by Ellie .
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?

You are close. You have an error:
Your step:
a_n = 21 + (n  1)  8
should be:
a_n = 21 + (n  1) * (8) 
oh yeah sorry i wrote that wrong i put 1688n but it still said my answer was wrong

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. 
i figured out what i was doing thank you so much!

You're very welcome.

arithmetic sequence
b_n=(2)^(n1)