Denote the key points as shown. Draw a segment of AO.
Consider the triangle AOB.
This triangle is right-angled, since the distance OB is the height (shortest distance).
AB is equal to half the length of the chord (according to the third property of the chord).
Then, by the Pythagorean theorem:
AO ^ 2 = OB ^ 2 + AB ^ 2
AO ^ 2 = 40 ^ 2 + (60/2) ^ 2
AO ^ 2 = 1600 + 900 = 2500
AO = 50 is the radius of the circle, therefore, the diameter D = 2 * AO = 100
Answer: D = 100
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.