Error writing Sec^2(x) -0.5 x in define function in C++

Okay I’m trying to make a root finder calculator and right now I was testing it out trigonometric functions. Now I’m getting errors whenever a sec is involved prompting either a "sec has not been defined"

Here’s what it looks like
Can someone explain to me whats wrong and how can I write "Sec^2(x)-0.5"

>Solution :

C++ standard library doesn’t provide secant function, you have to define it yourself.

double sec(double x)
{
    return 1 / cos(x);
}

Also, ^2 does not mean "square" in C++, it’s "bitwise XOR". You need to use * or pow:

sec(x) * sec(x) - 0.5;
pow(sec(x), 2) - 0.5;

And don’t use macros, they are going to bite you. Functions are much easier to use and will always behave as you expect:

double g(double x)
{
    return sec(x) * sec(x) - 0.5;
}