Two cylinder A and B of radii r and 2r are soldered co-axially. The free end of A is clamped and the free end of B is twisted by an angle `phi`. Find twist at the junction taking the material of tow cylinders to be same and of equal length.

Explanation

To solve the problem of finding the twist at the junction of two coaxially soldered cylinders A and B, we can follow these steps:

### Step 1: Understand the Setup
We have two cylinders:
- Cylinder A with radius \( r \)
- Cylinder B with radius \( 2r \)

Both cylinders are of equal length \( L \) and made of the same material. The free end of cylinder A is clamped, and the free end of cylinder B is twisted by an angle \( \phi \).
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