Math question - Circle from n straight lines or planes, end to end

Sure, so it's pretty straightforward if you're comfortable with geometry.

Drop this into an empty scene and play around with the inspector fields to see it work with different configurations. You should see something resembling:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class CircleFromLines : MonoBehaviour {
 
     public int sides = 6;
     public int radius = 7;
     public int z = 5;
 
     // We'll use cubes for this
     private List<GameObject> blocks;
 
     // Update is called once per frame
     void Recalculate()
     {
         // Create if necessary
         if (this.blocks == null)
             this.blocks = new List<GameObject>();
         
         // Clear if necessary
         for (int k=0; k<this.blocks.Count; k++)
             GameObject.Destroy(this.blocks[k]);
         
         // How far apart our pieces are from the center
         float innerAngle = 360f / this.sides;
 
         // Create them
         for (int k=0; k<this.sides; k++)
         {
             // Create the block
             var block = GameObject.CreatePrimitive(PrimitiveType.Cube);
 
             // Get position and the angle values
             int index = k % this.sides;
             float degrees = index * innerAngle;
             float radians = Mathf.Deg2Rad * degrees;
             float x = this.radius * Mathf.Cos(radians);
             float y = this.radius * Mathf.Sin(radians);
 
             // Determine their length
             float length = 2 * this.radius * Mathf.Abs(Mathf.Tan(Mathf.Deg2Rad * innerAngle / 2));
 
             // Then scale, rotate, and move them.  We'll keep all but one dimension small
             block.transform.localScale = new Vector3(0.2f, length, 0.2f);
             block.transform.rotation = Quaternion.Euler(0, 0, degrees);
             block.transform.position = new Vector3(x, y, this.z);
 
             this.blocks.Add(block);
         }
     }
 
     void OnGUI()
     {
         if (GUI.Button(new Rect(0, 0, 100, 50), "Recalculate"))
         {
             this.Recalculate();
         }
     }
 }