HP 42S - Manual (Page 10)

LN and ▀ e x : These functions calculate the base e=2.71828... logarithm and it's inverse.
Unlike LOG these are very, very important functions!
But what about if we want a logarithm in another base? It would be nice to have a special key for
this but it is just about remembering that
log
x
y =log
z
y /log
z
x where z is any other base.
If we take z=e=2.71828... we have
log
x
y =ln y/ln x .
Example: Calculate log
2
8
Answer: 8 LN 2 LN / which give us 3 because 2 3 =8 .
XEQ and ▀ GTO: These are related to programming and we shall discuss this later. XEQ will also
be discussed in ALPHA menu part.
STO and ▀ COMPLEX : These are related to the memories and complex numbers. We will
discuss this later.
RCL and ▀ % : RCL is related to memories and we will discuss later. ▀ % is the percentage
function. To calculate 10% of 300 we do
300 ENTER 10 ▀ % which gives 30 as answer.
Note that 300 remains in line y, so if you want to calculate 300 plus 10% you do
300 ENTER 10 ▀ % +
R↓ and ▀ π : We already discuss these. The first rows down the stack and the other returns
π=3.14...
SIN and ▀ ASIN : These are the sinus trigonometric function and its inverse. The angle type is set
up as said before in MODES menu. The default is degrees. ASIN is the inverse
usually called arcsine or sometimes sin
−1 . (don't confuse with cosec which is
1/sin). It is important to remember that ASIN is not a real function since there is
no single result. For example sin(135°)=sin(45°)=√2/2 but the calculator gives
always ASIN(√2/2)=45°. HP-42S will give a complex number if the input of an
arcsinus is bigger than 1 or smaller than -1.
COS and ▀ ACOS: These are the cosinus trigonometric function and its inverse.
TAN and ▀ ATAN: These are the tangent trigonometric function and its inverse. Not all numbers
can have a result for tangent. For example tan(90°) goes to infinite. The
HP-42S gives a big number instead.
ENTER and ▀ ALPHA: The ENTER key does not need any comment. ▀ ALPHA is the alpha-
numeric menu used to enter letters instead of numbers. When you press ▀
ALPHA what appears is