In `DeltaABC`, a=7, b=5 and c=8, then find the value of cos2B.

Explanation

To find the value of cos(2B) in triangle ABC where a = 7, b = 5, and c = 8, we can follow these steps:

### Step 1: Use the Cosine Rule to Find cos(B)
The cosine of angle B can be calculated using the formula:
\[ \cos B = \frac{a^2 + c^2 - b^2}{2ac} \]
Substituting the values of a, b, and c:
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