Probe a simple equation

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$L$ is the side of a square, and it is 10cm.

In the exercise I have a square shape which is cut with a semicircle in the bottom, and the radius of the semicircle is half the side of the square.

I need steps to prove that

$\displaystyle\frac{\pi L^2}{8} = \frac{\pi r^2}{2}$ (semicircle)

I eventually come to the place where both equations stay equal, 1/8 * Phi * L ² = 1/8 * Phi * L ², but Id like to know which steps I need to make the equation something like 1 = 1, so there's nothing more to do.

Thanks a lot.

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Note that, $\displaystyle r=\frac{L}{2}$ then replacement $r$, in $\displaystyle\frac{\pi r^2}{2}$ you obtain $\displaystyle\frac{\pi L^2}{8}$

Know that, the semicircle area is $\displaystyle\frac{\pi r^2}{2}$ how $\displaystyle r=\frac{L}{2}$ then:

$$\frac{\pi r^2}{2}=\frac{\pi (L/2)^2}{2}=\frac{\pi (L)^2}{4\cdot2}=\frac{\pi (L)^2}{8}$$

and is solved.