Sumation notation

Question

1)simplify the ratio of the factorials 30!/27!

      This is what i do 

     1•2•3•4•5...30/1•2•3•4•5•6....27=24,360

Is this answer right?

 2) use sigma notation to write the sum 

      [2]+[2•(1/2]+[2•(1/2)^2] +[2•(2/2)^3....[2•(1/2)^9

I think that n=(1/2)^9

    How you write the sigma greek leter in the key board

 

3)write an expresision for the most apparent sequence (Asume that n= 1

   5,7,9,11,13,15,19

     I am thinking that they increase by two but not when it get to 19

    So it can not be n+2

    I realy am notsure

Answer 1

If they're wanting you to "simplify", are they expecting you to cancel out the 27 x 26 x .... x 1 part, and then show only the 30 x 29 x 28 part?  (Which, yes, does equal 24,360.)

 

You make an Σ by hitting Alt-228.  It's an ASCII code.  This is just one of the billion places you can find these

http://chexed.com/ComputerTips/asciicodes.php

(Greek letters near the bottom.)

and there's other ways to do them but I think hitting Alt is the easiest.  (Also not sure if some of the other HTML codes work in some forums.)

Answer 2

Hi Daisy,

1) 30!/27!= 24,360

 

2) 2+[2*(1/2)]+[2*(1/2)^2+.........+[2*(1/2)^9]

   = 2*(1/2)º+[2*(1/2)]+[2*(1/2)^2]+.........+[2*(1/2)^9]

 

         n= 9

Ans:   Σ    2*(1/2)^n

         n=0 

 

3) 5,7,9,11,13,15,19

 

cane written as 1+4, 1+6 ,1+8,1+10,1+12,1+14,1+18

                     =1+2*2, 1+2*3, 1+2*4,1+2*5,1+2*6,1+2*7, 1+2*9

                     =1+2*i        where  i= 2,3,4,5,6,9

Ans:               =n+2*i         where n=1, i= 2,3,4,5,6,7,9.

 

Meena from Strongsville,OH

Answer 3

Oops, I see Meena already answered the question, so I deleted my response ...  ;-)