function roots( x ) {
		var f1;
		var f;
		var y;

		y = 1.0 - x;
		if ( y === 0.0 ) {
			return [ -BIG, -BIG ];
		}
		if ( x === 0.0 ) {
			return [ -BIG, -BIG ];
		}
		f = ln( x ) + ( a * ln( y ) ) + t;
		f1 = ( 1.0 / x ) - ( a / y );
		return [ f, f1 ];
	}
Calculates roots.

@private
@param {number} x - function value
@returns {Array} function roots