HP 48G - Manual (Page 59)

To decide which case it is, you should find the value of the expression
at the Sign Reversal point,
Exaiiiphn Find the value of the expression at the computed value of
X in order to decide whether it is a solution to R A T F U N C
or represents the location of a discontinuity.
S t e p 1 : Press to move the highlight to the EQ: field and press
E !-i F' F; =. The value of the expression at the computed value
of .(■ is returned to the stack.
S t e p 2 : Return to the stack to view the value of the expression
(labeled E x p r s ) ,
fCANCELl
{ HOME EXAMPLES EONS i
4:
3: X! 1.5
2:
a -
-3.00000000001
1: Expr: 133333333333
Because the value of the expression is not close to zero, in all
likelihood, there is a discontinuity at x = —3. (You can confirm
this by substituting -3 into the original equation and observing
that it generates denominators equal to zero—a sign of a potential
discontinuity.)
In general, whenever you expect multiple solutions, you’ll probably
save yourself some time and effort by plotting the expression and using
the graphical analysis tools instead of the SOLVE application (see
lesson 26 for an example).
Press frRfSOLVE) OK to return to the SOLVE application and try
solving another equation—this time keying it in yourself.
Exiiiiiplc': Find the measure (in degrees) of the largest angle in a
triangle with sides of 4, 7, and 9, with
9
as the largest
angle and c as the largest side). Use the Law of Cosines:
c“ = + 6“ — 2a6 cos
9
Solving Equations 5-5