The price system is a complex network composed of the prices of all the products bought and sold in the economy as well as of a great number of services.
(I)求A;
(Ⅱ)若BC边上的中线AM=2 2 ,高线AH= 3 ,求△ABC的面积.
在物理学史上,发现电流周围存在磁场的著名科学家是