Homework Help Forum: math

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+(n-1)d--so a_n=21+(n-1)-8 *a_n=-168-8n 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 -168-8n but it still said my answer was wrong

  
  

• math - Quidditch, Sunday, October 25, 2009 at 9:15pm

  a_n = 21 + (n-1)*(-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.

  
  

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