64 A Guide to Microsoft Excel 2007for Scientists and Engineers
Problems
The function NPER can be used to compute how many periods
needed for a certain scenario, and PMT gives the size of
deposit for another scenario. The function to compute how
is being applied to pay interest is IPMT, while PPMT tells
much is used to payoff the principal. The syntax for RATE
compute the needed rate for a certain financial scenario)
RATE(nper, pmt,
pv, fv, type, guess). The last argument may
strange. Look at the financial equation above and you will see
cannot be solved explicitly for
rate.
Excel needs to perform
iterative routine to get an answer. Generally we can omit
guess
argument. If the successive results of RATE do not
to within 0.0000001 after 20 iterations, RATE returns the #N
error value. Under these circumstances, we can try to assist
by giving a guess at the answer.
1.
*When you have tabulated data and no function but need
differential, the following formula may be used.
Forward
dy
=::
Y
1

Yo
dx
h
Backward
~j
dy
Yo

YI
dt
h
dx
2h
The voltage drop (V) across an inductance
(L)
is given by
V
=L
di
dt
In Figure 4.12 the central difference formula is used
interior points, and the forward and backward formulas
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 Fall '08
 Mc,F
 Trigraph, nd Engineers, certain financial scenario

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