Do it in coordinates. Suppose a is the origin, A (0 0,0), and the radius is set to 1. Write d, e and b respectively.

, c, p coordinates, where p(cosx, sinx) is the vector ap.

(added before the verb) means "negative" and "opposite"; (added before nouns to form verbs) means "get rid of", "get rid of"

Ac can be expressed. According to the relationship in the topic, we can list a set of ternary linear equations. We can express λ and μ from the angle of X, and then add them. There is only one variable, x, so we can find the extreme value of the function. It is better to explore the specific method by yourself, which is a good process of improving ability.