Defining distance between points

Dear Forum.
I’m new to Grasshopper…and after much fiddling, I’ve drawn a blank. Please can you help?
I’m trying to define a fixed point on a circle as a distance between two points (as shown in the attached image). I know the way I used ‘Eval’ is incorrect…but what else can I use?
The distance (20.992867 in this example) will be changeable thereby allowing the shifting of the point along a section of the circle’s circumference. (17.5 KB)
As background reference, the file is part of an origami project I’m working on.
Can anybody help resolve this problem?

Here’s a way that uses two spheres of radius ‘x’ that intersect with your circle. Each sphere intersects at two points so you get four points total, though only two that are unique. (21.9 KB)

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If approximate is good enough, you could find it this way, by carefully adjusting the slider until “goal” and “distance” match? (16.8 KB) (25.3 KB)

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Thank you very much Guys.
Awesome work.

Thanks again @Joseph_Oster and @anon39580149.
Your solutions both worked perfectly - thanks for sharing your time and insights. I’m incredibly impressed. I’m unsure how I’d manage with this forum…so much to learn.
Kind regards,