HP HP-15C

184 Section 13: Finding the Roots of an Equation
You have now found the two roots of f(x)
= 0. Note that this quadratic equation
could have been solved algebraically  and
you would have obtained the same roots
that you found using _.
G
G
r
The convenience and power of the _ key become more apparent
when you solve an equation for a root that cannot be determined
algebraically.
Example: Champion ridget hurler Chuck
Fahr throws a ridget with an upward
velocity of 50 meters/second. If the height
of the ridget is expressed as
h = 5000(1  e
t/20
)  200t,
how long does it take for it to reach the
ground again? In this equation, h is the
height in meters and t is the time in seconds.
Solution: The desired solution is the positive value of t at which h = 0.
Use the following subroutine to calculate the height.
Keystrokes
Display
| ¥
000–
´ bA
001–42,21,11
Begin with label.
2
002– 2
Subroutine assumes t is
loaded in X-and Y-registers.
0
003– 0
÷
004– 10