相除小于0,则相乘也小于0所以(x-3)(x+7)<0-7(x-3)/(x+7)<=0同理(x-3)(x+7)<=0-7<=x<=3分母不等于0所以-7
(x-3)(x+7)<0 -7(x-3)(x+7)<=0-7
大于-7小于3大于等于-7小于等于3