编写一个程序,计算平面应力状态及空间应力状态的主应力,最大剪应力,如为平面应力状态则需输出方位角agl斜截面上的应力及主方向角，画出应力圆示意图。

已知二向应力状态，ax=10MPa,ay=-20MPa,bxy=15MPa,agl=45,求主应力，最大切应力，斜截面上的应力，作出应力圆示意图。-The preparation of a program to calculate the plane stress state and stress state space of principal stress, maximum shear stress, such as the need for the plane stress state of the output azimuth agl stress on the inclined section and the main direction angle, draw stress circle diagram. Second, the stress state is known, ax = 10MPa, ay =- 20MPa, bxy = 15MPa, agl = 45, for principal stress, maximum shear stress, the stress on the inclined section to stress circle diagram.