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This is my first LaTeX document.

Suppose we are given a rectangle with side lengths $(x+1)$ and $(x+3)$. Then the equation $A=x^2+4x+3$ represents the area of the rectangle.

Suppose we are given a rectangle with side lengths $(x+1)$ and $(x+3)$. Then the equation $$A=x^2+4x+3$$ represents the area of the rectangle.
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