Show that the coefficient of area expansions `(Delta A//A)//Delta T` of a rectangular sheet of the solid is twice its linear expansivity `alpha`.

Explanation

To show that the coefficient of area expansion \((\Delta A/A)/\Delta T\) of a rectangular sheet of solid is twice its linear expansivity \(\alpha\), we can follow these steps:

### Step 1: Define the Initial Area
Let the initial dimensions of the rectangular sheet be:
- Length \(L\)
- Breadth \(B\)

Thus, the initial area \(A\) is given by:
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