Design a graph, find the value of 1 + 3 + 5 + 7 + 9 +. + (2n-1), a is a positive integer, and use the graph to make the necessary explanation

Design a graph, find the value of 1 + 3 + 5 + 7 + 9 +. + (2n-1), a is a positive integer, and use the graph to make the necessary explanation

As shown in the figure, every time the value increases, the square will be expanded outward once