HP HP-21 - Using T

Using 7
m, 3.141592654, is provided as a fixed constant in the HP-21.
Merely press 8 (7] whenever you need it in a calculation
before executing the applicable operation.
Example 1: Calculate 3.
Press Display
3ENER
Example 2: Find the area A of a circle with 3-foot radius r,
where
A
r
I
T2
3
Solution:
Press Display
3 ]
=
[x] Square feet.
Example 3: Finding himself wafted dangerously close to a
series of jagged mountain peaks, intrepid balloonist Ike Dae-
dalus frantically cranks open the helium valve on his spherical
balloon. Gas from the helium tank increases the balloon’s radius
from 25 feet to 27 feet, and Daedalus safely clears the mountain-
tops. By how much did Daedalus increase the volume of the
balloon?
Solution: Volume of a sphere is equal to 4/3z7r3. The increase
in volume is therefore (4/3) 7 (27)% minus (4/3) = (25)3. This can
also be written
s 27 — (250 ]
Press Display
27 3
25 3 N
B
4&