Please teach!!! How can you change a point along a Arc?

Hi,Nice to meet you.

I made it to the place where a line became the Arc.

I want to move it so that the points on the Arc gather in the center point of Arc along a Arc.

But the distance of the point is constant at the time of line.

If it becomes the Arc from the line and what should do to collect points in the center of the Arc?

I make it with grasshopper0.8.