Commodore Plus 4 - Page 185

Redefining the Function Keys 173
square a number by multiplying it by itself, get a square root by using the SQR
function, and calculate a reciprocal by dividing 1 by the number.
It is somewhat faster to add a number to itself than to multiply by 2. It is
somewhat faster to divide by 2 than to multiply by 0.5. Subtraction and addition
take virtually the same amount of time.
Logarithms and Exponentials LOG(X) returns the logarithm base e (the natu
ral logarithm) of X. The logarithm with respect to a different base, B, can be
found by dividing LOG(X) by LOG(B). The inverse of the logarithm base e (e
raised to a power) can be calculated with EXP. The inverse of the logarithm base
B can be calculated by using the up arrow to raise B to the power.
Trigonometric Calculations An approximation of pi is available by using the
pi key (the Q and equal keys pressed together). This is particularly useful when
the values of trigonometric ratios are desired and the angle is measured in
degrees. The SIN, COS, and TAN functions are available, but each requires the
specified angle to be measured in radians. To translate from degrees to radians,
multiply the angle by pi, and divide by 180.
To calculate the values of the remaining trigonometric ratios, recall that
csc(X) = 1/SIN(X)
sec(X) = 1/COS(X)
cot(X) = 1/TABT(X)
The only inverse trigonometric ratio available is the arctangent (ATN). The value
is returned in radians. To change to degrees, multiply by 180, and divide by pi. To
calculate the values of the remaining inverse functions, recall that
arcsin(A) = ATN(A/SQR( 1-A*A))
arccos(A) = ATW(SQR( 1-A*A)/A)
arccsc(A) = ATN(l/(A*SQR(l-l/(A*A))))
arcsec(A) = ATN(A*SQR(1-1/(A*A)))
arccot(A) = ATN(1/A)
Rounding Off Numbers When asked to display a number, the PRINT (or
PRINT#) command prints nine digits of precision. If this is not desired, the
PRINT USING command may be used. Or, recall that the number X rounded to
N decimal places is given by
IET(10tW*X+.5)/10t]!ir