Label the squares and rectangles in given figure so that it represents $(a + b + c)^2 = a^2 + b^2 + c^2 + 2ab + 2bc + 2ca$ . [Page No. 76]

The big square has side $(a + b + c)$. Splitting each side into the parts $a, b, c$ makes a $3 \times 3$ grid of nine regions.
Label each region by (its row length) $\times$ (its column length):

Consider a square of side length $(a + b + c)$. When it is divided into smaller regions, the three squares along the diagonal have areas $a^2, b^2, c^2$ giving a total area of $a^2 + b^2 + c^2$.

The remaining regions are rectangles with areas $ab, bc$, and $ca$. Each rectangle appears twice in the figure, contributing $2ab + 2bc + 2ca$.

Adding the areas of all the regions, we obtain $(a + b + c)^2 = a^2 + b^2 + c^2 + 2ab + 2bc + 2ca$.