可以两边减去32a=2b两边同除以2a=b
(a²-ab)+(ab-b²)=18+(-12)a²-b²=6(a²-ab)-(ab-b²)=18-(-12)a²-2ab+b²=30 说说思路圆心A(-D/2,-E/2)半径平方(D²+E²-4F)/4则勾股定理切线长²=PA²-半径²=(m+D/2²+(n+E/2)²-(D²+E²-4F)/4
