@Evica
Background info: We’re going to use trig. Don’t worry, we’re here to help make it easier!

Step 1:
Rotate points A4, A5, and A3 around point A1 by angle

**radTodeg( 2 * asin( (y/2) / (2 * Line_A1_A3) ) )** using the Rotate tool.
This finds the central angle given chordlength and radius. Original formula is sin(theta) = opposite/hypoteneuse, but only for half the chordlength, so we have to multiply by 2 then find the arcsine then convert to degrees etc. Don’t worry about it We really need a tool that does this easily.

If typing in asin gives you errors, click on the f(x) symbol and select the Functions radio button then select asin from the list.
This example we use 3 instead of your (y/2):

Step 2: Move the center section down.

a. Draw point A8 with Point from X and Y, using A4 for vertical line and A4a1 horizontal line.

b. Then draw a line from A4 to A8 using the Line Between Points tool.

c. Use the Move tool to move Points A, A2 and A5 down length Line_A4_A8 at angle 270

d. Draw lines between your new points with the Line Between Points Tool

We could have moved the center section down and over to meet up with A4a1, but then we would have had to draw a new center line. Both approaches yield similar results.

Let us know how this works for you!
HTH