令α=[arc tg B/(A-C)]/2
x=Xcosα-Ysinα
y=Xsinα+Ycosα
代入后原方程化为
aX²+cY²+dX+eY+f=0
画出这个椭圆,然后反方向旋转α角度即可.aX²+cY²+dX+eY+f=0椭圆怎么画呢？aX²+cY²+dX+eY+f=0aX²+dX+cY²+eY+f=0aX²+dX+d²/(4a)+cY²+eY+e²/(4c)=d²/(4a)+e²/(4c)-fa(X+d/2a)²+c(Y+e/2c)²=(cd²+ae²-4acf)/(4ac)(X+d/2a)²/c+(Y+e/2c)²/a=(cd²+ae²-4acf)/(4a²c²)