In `DeltaABC`, a=4, b=5 and c=6, prove that the greatest angle is twice the least angle.

Explanation

To prove that in triangle \( \Delta ABC \) with sides \( a = 4 \), \( b = 5 \), and \( c = 6 \), the greatest angle \( C \) is twice the least angle \( A \), we will use the cosine rule and some trigonometric identities.

### Step-by-Step Solution:

1. **Identify the Angles**:
- The sides of the triangle are given as \( a = 4 \), \( b = 5 \), and \( c = 6 \).
- The greatest angle is opposite the longest side, which is \( c \). So, \( C \) is the greatest angle.
- The least angle is opposite the shortest side, which is \( a \). So, \( A \) is the least angle.
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