HP 39gs Master Manual page 180

LINEAR?(<expression>,<var.name>)
This is another of those functions which is probably aimed more at the programmer than at the normal user. It
is designed to test whether a supplied expression is linear or non-linear in the variable you specify, returning
zero for non-linear and 1 for linear.
Eg. Suppose we use the expression AX − B + 4
If X is the variable and A and B are both constants (say
the expression AX − + 4 would become 4 X
2
B
non-linear. Thus
LINEAR?
On the other hand, if X were one of the constants (say
the variable, then the expression AX − + 4 would become
− + 4 or 36A − 1 , which is linear. Thus
A ×
2
6 5
a value of as shown right.
1
The main use for this is going to be when a programmer does not know
in advance what function the user is going to type in.
QUAD(<expression>,<var.name>)
This function uses the quadratic formula x =
roots of a quadratic, using the '
symbol. The quadratic is entered as an expression, and you must
indicate which variable is being solved for, since you could have an
equation such as Px + Qx − =
2
and you would need to specify to solve for
not or .
P Q
Eg. Solve x − − = 0
2
4 x 5
Use
QUAD(X2-4X-5,X)
Answer:
(4+S1*6)/2
It is now up to you to interpret this algebraically as:
If you are simply after the roots of the quadratic then it is far better to use the
298) or to graph the function and use the
2
− 5 + 4 which would be
2
returns zero (right).
2
B
LINEAR?
− ± − 4 ac
b b
2 a
' formal variable to represent the
S1
where and were memory values,
P Q
5 0
in order to tell the calculator that the active variable was
X
tools.
) then
A=4, B=5
) and A were
X=6
would return
2
to give both
±
±
4 6
x =
2
+ 4 − 6
4 6
=
or
2
= 5 or −1
180
2
function (page
POLYROOT
and
X