题目

Long nights of winter can leave even the most positive people feeling cranky（古怪的）. But for about 5% of Americans, it’s more serious: Seasonal affective disorder (SAD) is a type of depression that most occurs in the winter. Symptoms include loss of energy, eating more and difficulty concentrating. The cause of SAD is unknown, but darker days probably play a role. Reduced levels of natural sunlight can disrupt your body’s internal clock, which can lead to depression. It also causes a drop in serotonin（血清素）, a feel-good brain chemical. Severe cases may need antidepr(13分) 已知函数。    （I）当时，求曲线在点处的切线方程；    （Ⅱ）当函数在区间上的最小值为时，求实数的值；    （Ⅲ）若函数与的图象有三个不同的交点，求实数的取值范围。