(X-50)[120-6*(X-50)/5]=6750
问题描述：
(X-50)[120-6*(X-50)/5]=6750
答
(x-50)(180-6x/5)=6750
(x-50)(x-150)=-5625
x²-200x+13125=0
显然无解
答
(x-50)(180-6x/5)=6750
(x-50)(x-150)=-5625
x²-200x+13125=0
用b²-4ac=...