Mathematical quadratic function, how to find the parameter range of quadratic function with a parameter in a given closed interval, thank you.

1. 1. Find the range of quadratic function solution according to b2-4ac is greater than or equal to 0;

2. According to factorization and other methods, two possible roots A and B of quadratic function are found;

3. Suppose the given closed interval is [c, d];

4. Consider two scenarios:

A is greater than or equal to c, and b is less than or equal to d; A is less than or equal to b;

B is greater than or equal to c, a is less than or equal to d, and b is less than or equal to a;

According to these two situations and the scope of solution, find the intersection.