Puzzle 27 Find the blue area.

[ttokoro]

We have a circle with r=10 cm. Solve the blue area of Octagon and Square make the shape.
This is able to find without trigonometric function or Junior high school knowledge.
But we can use Mathcad to solve.

[Werner_E · Accepted solution]

Too easy for Mathcad, even for Prime!

OR

[ttokoro]

Without using trigonometric functions.

[ppal]

Using Solve Box