$(a+b)(a-b) \,=\, a^2-b^2$
$a$ and $b$ are two literals. They form two binomials $a+b$ and $a-b$ by summation and subtraction respectively. The product of them is written as $(a+b)(a-b)$ in mathematics. Its expansion is equal to $a^2-b^2$. It is used as an algebraic identity in mathematics and can be derived in geometrical approach in three simple steps on the basis of areas of square and rectangle.
The width of the upper rectangle is $a-b$ and the length of the lower rectangle is also $a-b$ geometrically. If the lower rectangle is rotated by $90^\circ$, then the lengths of both rectangles become same and it is useful to join them together as a rectangle.
In first step, it is derived that the area of the subtracted shape as $a^2-b^2$ but in this case, the area of the big rectangle is determined as $(a+b)(a-b)$.
In fact, the subtracted figure is transformed as a big rectangle. Thus, the areas of both geometric shapes should be equal geometrically.
$\,\,\, \therefore \,\,\,\,\,\, (a+b)(a-b) \,=\, a^2-b^2$
Geometrically, it is proved that the product of the binomials $a+b$ and $a-b$ is equal to $a^2-b^2$.
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