Express the following in summation notation

Question

a. x1+x2+x3+x4+x5

 

b. x1+2x2+3x3+4x4+5x5

 

Answer 1

a. ∑⁵_n=1 x_n

b. ∑⁵_n=1nx_n

If the 1 in x1 (or 2 in x2) is supposed to be an exponent, then picture making the subscripts superscripts as in:

∑⁵_n=1 xⁿ