code: function cross( x, y ) {
  	if ( !Array.isArray( x ) ) {
  		throw new TypeError( 'cross()::invalid input argument. First argument must be an array.' );
  	}
  	if ( !Array.isArray( y ) ) {
  		throw new TypeError( 'cross()::invalid input argument. Second argument must be an array.' );
  	}
  	if ( x.length !== 3 || y.length !== 3 ) {
  		throw new Error( 'cross()::invalid input argument. Input arrays must be of length 3.' );
  	}
  	return [
  		x[1]*y[2]-x[2]*y[1],
  		x[2]*y[0]-x[0]*y[2],
  		x[0]*y[1]-x[1]*y[0]
  	];
  }
docs: CROSS PRODUCT // 
  FUNCTION: cross( x, y )
  Computes the cross product between two numeric arrays.
  
  @param {Array} x - numeric array
  @param {Array} y - numeric array
  @returns {Number} cross product