Question 887613
<pre>
a) 2+5+10+14+18

We can't put that in sigma notation because there is no obvious pattern
to those numbers as there is for (b) and (c).  Are you sure you copied (a)
right?

I see that the other tutor assumed you meant 6 instead of 5.  Then it's 

2+6+10+14+18 = 4-2,8-2,12-2,16-2,20-4.  Each term is 2 less than a multiple
of 4 or 4k-2 

{{{sum((4k-2),k=1,matrix(1,2,"",5))}}}

b) 5+25+125+625.  That's {{{5^1+5^2+5^3+5^4}}}.  Each term is of the form {{{5^k}}} where k goes from 1 to 4 

{{{sum((5^k),matrix(1,2,"",k=1),matrix(1,3,"","",4))}}}


c) 1/2+1/2×3+1/3×4+...+1/99×100

That's {{{1/(1*2)+1/(2*3)+1/(3*4)+""*""*""*""+1/(99*100)}}}.  Each term
is of the form {{{1/(k*(k+1))}}} where k goes from 1 to 99.

{{{sum( ( 1/(k*(k+1)) ),matrix(1,2,"",k=1),matrix(1,3,"","",99)  )}}}

Edwin</pre>