Find all zeroes of these functions,and any values of x where the function is discontinuous.Then analyse the sign of the function by taking test points around these zeroes and discontinuities.

• 找到这个函数所有的零点以及所有的不连续点，并利用在这些零点和不连续点两边选取测试点的方法对函数的取值正负进行分析。