HP 49g+ - Manual (Page 142)

Page 12-1
Chapter 12
Multi-variate Calculus Applications
Multi-variate calculus refers to functions of two or more variables. In this
Chapter we discuss basic concepts of multi-variate calculus: partial derivatives
and multiple integrals.
Partial derivatives
To quickly calculate partial derivatives of multi-variate functions, use the rules
of ordinary derivatives with respect to the variable of interest, while
considering all other variables as constant. For example,
( ) ( )
) sin( ) cos( ), cos( ) cos( y x y x
y
y y x
x
− =
∂
∂
=
∂
∂
,
You can use the derivative functions in the calculator: DERVX, DERIV, ∂ ,
described in detail in Chapter 11 of this Guide, to calculate partial derivatives
(DERVX uses the CAS default variable VX, typically, ‘X’). Some examples of
first-order partial derivatives are shown next. The functions used in the first
two examples are f(x,y) = SIN(y), and g(x,y,z) = (x
2 +y 2 ) 1/2 sin(z).