function binet( x ) {
	var a;
	var b;
	if (
		isnan( x ) ||
		x === PINF ||
		x === NINF
	) {
		return NaN;
	}
	a = pow( PHI, x );
	b = cospi( x ) / a;
	return ( a - b ) / SQRT_5;
}
Evaluates Binet's formula extended to real numbers.

## Notes

-   [Non integer Fibonacci numbers][1]
-   [Interpolated Fibonacci numbers - real or complex][2]

[1]: https://math.stackexchange.com/questions/798190/non-integer-fibonacci-numbers
[2]: https://math.stackexchange.com/questions/589841/interpolated-fibonacci-numbers-real-or-complex

@param {number} x - input value
@returns {number} real-valued result

@example
var y = binet( 0.0 );
// returns 0.0

@example
var y = binet( 1.0 );
// returns 1.0

@example
var y = binet( 2.0 );
// returns 1.0

@example
var y = binet( 3.0 );
// returns 2.0

@example
var y = binet( 4.0 );
// returns 3.0

@example
var y = binet( 5.0 );
// returns ~5.0

@example
var y = binet( 6.0 );
// returns ~8.0

@example
var y = binet( NaN );
// returns NaN

@example
var y = binet( 3.14 );
// returns ~2.12

@example
var y = binet( -1.0 );
// returns 1.0