Radio Shack TRS-80 User Manual page 163

repeat the process until
you
find the
right tree ... or surrender to
frostbite.
Or you
can
use
a
little
trigonometry.
Trigonometry
will let
you
figure
the
height, H, of the
tree
from two
simple
facts:
your
distance,
D,
from
the base of the
tree,
and
the angle, A, between
the base
and
tip
of the
tree as
measured from
the point at
which
you're standing:
If
you're standing
as
indicated in the drawing, then
H
= D*TAN(A)
(That's
"H
equals
D
times the tangent of angle A.")
Here's
where
the
TRS-80 comes
in.
(You'll also
need
a
very long extension
cord
to
run from
the nearest
electrical outlet to the
site
of the
tree.)
TAN(X)
is
one
of the trigonometric functions
available
as
a subroutine
for the TRS-80.
Turn
to
page 218
of
Appendix
A
and
find the Tangent
Subroutine.
(It's
the longest of the
"trig"
subroutines, because
it
actually contains
two
of the
others, Sine
and
Cosine).
Type
NEW
to clear out
the
program
memory
and
carefully
type
in
the tangent subroutine
(steps
30300
to
30455). Be
sure to
add
a protective
END
block:
30000 END
Now
type
in
the following
program:
1 tar
IN.
"HOW
FAR ARE YOU FROM BASE OF TREE";D
20 IN.
"WHAT
IS ANGLE BETWEEN TIP AND BASE OF
TREE";A
30
X=A:GOSUB 30320
40 H=INT( D*Y+
.5
)
50 IF
H=28 THEN
80
60
P.
"FIND ANOTHER
TREE
—
THIS ONE IS"sH; "FEETTALL."
?A
,!»,
161