A <function_call> has a lower precedence than an <operand>, but it has a higher precedence than all the math, comparison, and logical operations. This means you have to be careful about correctly parenthesizing function arguments.
sin x + 1
is evaluated as:
(sin x) + 1
In general, you have to put arguments that are expressions inside parentheses,
sin (x + 1)
atan2 (y - 1) (z - 1)
This rule has one exception, the unary minus. It is recognized as one type of <operand> you don’t have to parenthesize.
is interpreted as: