[Math] Find the area of a circle part of which is in a square

areageometry

I have a square with sides of 10cm and I have a circle with radius of 6cm. Now I've to find the area of the circle that is inside of the square.Here is the graph
enter image description here

I had an idea of finding the area of the arc(90 degrees) and subtracting it from 25(100/4), but then I noticed that the area of arc would still include the areas which are outside of the square.

Best Answer

Hint: You can use the image to get the intuition. Also remember that a circle is defined as $x^2+y^2=r^2$

enter image description here

Circle intersects square at $(\sqrt{11},5)$ and $(5,\sqrt{11})$, thus you have triangles with areas: $$A_{\triangle}=\frac12(5)(\sqrt{11})$$ The area of the sector is given by: $$A_{\text{sector}}=\pi r^2\cdot\frac{\theta}{360}=\pi(6^2)\cdot\frac{90-2\sin^{-1}\frac{\sqrt{11}}6}{360}$$ Thus you get the area you need: $$A=4(2\cdot A_{\triangle}+A_{\text{sector}})$$