Calculus 5.1

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5.1 Estimating with Finite Sums
Greenfield Village, Michigan
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Consider an object moving at a constant rate of 3
ft/sec.
Since rate . time distance
If we draw a graph of the velocity, the distance
that the object travels is equal to the area
under the line.
After 4 seconds, the object has gone 12 feet.
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If the velocity is not constant, we might guess
that the distance traveled is still equal to the
area under the curve.
(The units work out.)
Example
We could estimate the area under the curve by
drawing rectangles touching at their left corners.
This is called the Left-hand Rectangular
Approximation Method (LRAM).
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We could also use a Right-hand Rectangular
Approximation Method (RRAM).
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Another approach would be to use rectangles that
touch at the midpoint. This is the Midpoint
Rectangular Approximation Method (MRAM).
In this example there are four subintervals. As
the number of subintervals increases, so does the
accuracy.
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With 8 subintervals
width of subinterval
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Inscribed rectangles are all below the curve
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We will be learning how to find the exact area
under a curve if we have the equation for the
curve. Rectangular approximation methods are
still useful for finding the area under a curve
if we do not have the equation.
The TI-89 calculator can do these rectangular
approximation problems. This is of limited
usefulness, since we will learn better methods of
finding the area under a curve, but you could use
the calculator to check your work.
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If you have the calculus tools program installed
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Note We press alpha because the screen starts in
alpha lock.
Make the Lower bound 0 Make the Upper bound
4 Make the Number of intervals 4
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