Creating second arch from tangent of first arch

Hi there, 

Very new to grasshopper, and was wondering if I could get some help on lining up some arches. 

I want a series of parabolic/catenary arches. The first arch is symmetrical and spans along a curve. I want the second arch to extend in the following directions: 

From the tangent between the inner arch or, 

Continuing to extend at the same angle of the right inner arch. 

I have done some basic experimenting, however the arches that i have made do not meet at the same angle, which i i'm not sure if it would be structurally stable. 

Thanks

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