Square

The diagram below consists of a small square, four equilateral triangles, and a large square.  Find the area of the large square.   

At the base of the triangles, extend the line on over to the right side of the square.  

That line is 2 & ¹/₂ triangle bases long.  The base of each triangle is one unit.  

So the width of the large square is 2 & ¹/₂ units.  

Two and a half squared is six and a quarter.  The area of the large square is 6.25 units².   

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