<?php
/* This answer contains all the math functions in PHP, and all the
predefined math constants */
# Math Functions
abs() Returns the absolute (positive) value of a number
acos() Returns the arc cosine of a number
acosh() Returns the inverse hyperbolic cosine of a number
asin() Returns the arc sine of a number
asinh() Returns the inverse hyperbolic sine of a number
atan() Returns the arc tangent of a number in radians
atan2() Returns the arc tangent of two variables x and y
atanh() Returns the inverse hyperbolic tangent of a number
base_convert() Converts a number from one number base to another
bindec() Converts a binary number to a decimal number
ceil() Rounds a number up to the nearest integer
cos() Returns the cosine of a number
cosh() Returns the hyperbolic cosine of a number
decbin() Converts a decimal number to a binary number
dechex() Converts a decimal number to a hexadecimal number
decoct() Converts a decimal number to an octal number
deg2rad() Converts a degree value to a radian value
exp() Calculates the exponent of e
expm1() Returns exp(x) - 1
floor() Rounds a number down to the nearest integer
fmod() Returns the remainder of x/y
getrandmax() Returns the largest possible value returned by rand()
hexdec() Converts a hexadecimal number to a decimal number
hypot() Calculates the hypotenuse of a right-angle triangle
intdiv() Performs integer division
is_finite() Checks whether a value is finite or not
is_infinite() Checks whether a value is infinite or not
is_nan() Checks whether a value is 'not-a-number'
lcg_value() Returns a pseudo random number in a range between 0 and 1
log() Returns the natural logarithm of a number
log10() Returns the base-10 logarithm of a number
log1p() Returns log(1+number)
max() Returns the highest value in an array, or the highest value of several specified values
min() Returns the lowest value in an array, or the lowest value of several specified values
mt_getrandmax() Returns the largest possible value returned by mt_rand()
mt_rand() Generates a random integer using Mersenne Twister algorithm
mt_srand() Seeds the Mersenne Twister random number generator
octdec() Converts an octal number to a decimal number
pi() Returns the value of PI
pow() Returns x raised to the power of y
rad2deg() Converts a radian value to a degree value
rand() Generates a random integer
round() Rounds a floating-point number
sin() Returns the sine of a number
sinh() Returns the hyperbolic sine of a number
sqrt() Returns the square root of a number
srand() Seeds the random number generator
tan() Returns the tangent of a number
tanh() Returns the hyperbolic tangent of a number
# Predefined Math Constants
INF INF The infinite
M_E 2.7182818284590452354 Returns e
M_EULER 0.57721566490153286061 Returns Euler constant
M_LNPI 1.14472988584940017414 Returns the natural logarithm of PI: log_e(pi)
M_LN2 0.69314718055994530942 Returns the natural logarithm of 2: log_e 2
M_LN10 2.30258509299404568402 Returns the natural logarithm of 10: log_e 10
M_LOG2E 1.4426950408889634074 Returns the base-2 logarithm of E: log_2 e
M_LOG10E 0.43429448190325182765 Returns the base-10 logarithm of E: log_10 e
M_PI 3.14159265358979323846 Returns Pi
M_PI_2 1.57079632679489661923 Returns Pi/2
M_PI_4 0.78539816339744830962 Returns Pi/4
M_1_PI 0.31830988618379067154 Returns 1/Pi
M_2_PI 0.63661977236758134308 Returns 2/Pi
M_SQRTPI 1.77245385090551602729 Returns the square root of PI: sqrt(pi)
M_2_SQRTPI 1.12837916709551257390 Returns 2/square root of PI: 2/sqrt(pi)
M_SQRT1_2 0.70710678118654752440 Returns the square root of 1/2: 1/sqrt(2)
M_SQRT2 1.41421356237309504880 Returns the square root of 2: sqrt(2)
M_SQRT3 1.73205080756887729352 Returns the square root of 3: sqrt(3)
NAN NAN Not A Number
PHP_ROUND_HALF_UP 1 Round halves up
PHP_ROUND_HALF_DOWN 2 Round halves down
PHP_ROUND_HALF_EVEN 3 Round halves to even numbers
PHP_ROUND_HALF_ODD 4 Round halves to odd numbers
<?//thank you rahmatjon
Example:
<?php
$arg=0.5;
$val=acos($arg);
echo "acos(" . $arg . ") = " . $val . " radians.<br/>";
echo "Pi value = " . pi() . "<br/>";
echo "acos(" . $arg . ") = " . $val/pi()*180 . " degrees<br/>";
?>