Riemann Sums

Definition (Riemann Sum) A Riemann sum for a function riemann sums _gr_1.gif] on the closed bounded interval riemann sums _gr_2.gif] is a sum of the form

riemann sums _gr_3.gif]

where

riemann sums _gr_4.gif]

and for, riemann sums _gr_5.gif]

riemann sums _gr_6.gif]    and      riemann sums _gr_7.gif]

The set riemann sums _gr_8.gif] is called a partition of riemann sums _gr_9.gif] and the largest of the riemann sums _gr_10.gif] is called the norm of riemann sums _gr_11.gif].

Example (Riemann Sum) Given the function riemann sums _gr_12.gif] the closed bounded interval riemann sums _gr_13.gif] and the partition riemann sums _gr_14.gif] compute a Riemann sum.

    Solution. Organizing into a table we compute the values,  

riemann sums _gr_15.gif]

So the Riemann sum for these riemann sums _gr_16.gif] is

riemann sums _gr_17.gif]

riemann sums _gr_18.gif]
  
riemann sums _gr_19.gif]

riemann sums _gr_20.gif]
   riemann sums _gr_21.gif]

Example (Riemann Sum and Area) Use a Riemann sum to approximate the area under the graph of riemann sums _gr_22.gif] on riemann sums _gr_23.gif] with 8 subintervals.

    Solution. As a partition we choose, riemann sums _gr_24.gif] Organizing our computations and choices for our subinterval representations we have,   
    
riemann sums _gr_25.gif]

So the Riemann sum for this partition riemann sums _gr_26.gif] and these riemann sums _gr_27.gif] is

riemann sums _gr_28.gif]

riemann sums _gr_29.gif]
   riemann sums _gr_30.gif]

Example (Riemann Sum and Area) Use a Riemann sum to approximate the area under the graph of riemann sums _gr_31.gif] on riemann sums _gr_32.gif] with 10 subintervals.

    Solution. As a partition we choose,
    
riemann sums _gr_33.gif]
    
Organizing our computations and choices for our subinterval representations we have,   
    
riemann sums _gr_34.gif]


riemann sums _gr_35.gif]
   riemann sums _gr_36.gif]

Cite this as:
Riemann Sums
Published by Library of Math -- Online math organized by subject into topics.
Written by Smith, David A.
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