After https://ask.sagemath.org/question/45463/solvex-does-not-fully-isolate-x-how-can-i-help-along/ I substituted variables with numbers (in RIF format) so that sage might have an easier time solving for d_k. I got this:

```
0 == -v_ges + 1/(sqrt(4*d_k^2 + 0.57?)*d_k*((3.?e-11)/(d_k - 0.1?) + 1.?e-8)) - 1/(sqrt(4*d_k^2 + 0.0625000000000000)*d_k*((3.?e-11)/(d_k - 0.1?) + 1.?e-8)) + 3.7?e9
```

But now, when I try to solve the above for d_k, I get this long traceback, which is above my sage skills. How can I solve this? The worksheet is https://cocalc.com/share/f7766c5e-2f4d-4916-bb0d-74a7182e5fd5/2019-02-09-203517.sagews?viewer=share

```
*** WARNING: Code contains possible implicit multiplication ***
*** Check if any of [ 5e, 5e ] need a "*" sign for multiplication, e.g. 5x should be 5*x ! ***
Error in lines 42-42
Traceback (most recent call last):
File "/cocalc/lib/python2.7/site-packages/smc_sagews/sage_server.py", line 1188, in execute
flags=compile_flags) in namespace, locals
File "", line 1, in <module>
File "sage/symbolic/expression.pyx", line 11568, in sage.symbolic.expression.Expression.solve (build/cythonized/sage/symbolic/expression.cpp:59905)
return solve(self, x, multiplicities=multiplicities,
File "/ext/sage/sage-8.6_1804/local/lib/python2.7/site-packages/sage/symbolic/relation.py", line 1044, in solve
return _solve_expression(f, x, explicit_solutions, multiplicities, to_poly_solve, solution_dict, algorithm, domain)
File "/ext/sage/sage-8.6_1804/local/lib/python2.7/site-packages/sage/symbolic/relation.py", line 1282, in _solve_expression
m = ex._maxima_()
File "sage/symbolic/expression.pyx", line 817, in sage.symbolic.expression.Expression._maxima_ (build/cythonized/sage/symbolic/expression.cpp:7898)
return super(Expression, self)._interface_(maxima)
File "sage/structure/sage_object.pyx", line 663, in sage.structure.sage_object.SageObject._interface_ (build/cythonized/sage/structure/sage_object.c:5290)
s = init_func()
File "sage/structure/sage_object.pyx", line 769, in sage.structure.sage_object.SageObject._maxima_lib_init_ (build/cythonized/sage/structure/sage_object.c:7971)
return self._maxima_init_()
File "sage/structure/sage_object.pyx", line 762, in sage.structure.sage_object.SageObject._maxima_init_ (build/cythonized/sage/structure/sage_object.c:7742)
return self._interface_init_(I)
File "sage/symbolic/expression.pyx", line 854, in sage.symbolic.expression.Expression._interface_init_ (build/cythonized/sage/symbolic/expression.cpp:8069)
return InterfaceInit(I)(self)
File "/ext/sage/sage-8.6_1804/local/lib/python2.7/site-packages/sage/symbolic/expression_conversions.py", line 219, in __call__
return self.relation(ex, operator)
File "/ext/sage/sage-8.6_1804/local/lib/python2.7/site-packages/sage/symbolic/expression_conversions.py", line 471, in relation
self(ex.rhs()))
File "/ext/sage/sage-8.6_1804/local/lib/python2.7/site-packages/sage/symbolic/expression_conversions.py", line 217, in __call__
return self.arithmetic(ex, operator)
File "/ext/sage/sage-8.6_1804/local/lib/python2.7/site-packages/sage/symbolic/expression_conversions.py", line 624, in arithmetic
args = ["(%s)"%self(op) for op in ex.operands()]
File "/ext/sage/sage-8.6_1804/local/lib/python2.7/site-packages/sage/symbolic/expression_conversions.py", line 217, in __call__
return self.arithmetic(ex, operator)
File "/ext/sage/sage-8.6_1804/local/lib/python2.7/site-packages/sage/symbolic/expression_conversions.py", line 624, in arithmetic
args = ["(%s)"%self(op) for op in ex.operands()]
File "/ext/sage/sage-8.6_1804/local/lib/python2.7/site-packages/sage/symbolic/expression_conversions.py", line 217, in __call__
return self.arithmetic(ex, operator)
File "/ext/sage/sage-8.6_1804/local/lib/python2.7/site-packages/sage/symbolic/expression_conversions.py", line 624, in arithmetic
args = ["(%s)"%self(op) for op in ex.operands()]
File "/ext/sage/sage-8.6_1804/local/lib/python2.7/site-packages/sage/symbolic/expression_conversions.py", line 217, in __call__
return self.arithmetic(ex, operator)
File "/ext/sage/sage-8.6_1804/local/lib/python2.7/site-packages/sage/symbolic/expression_conversions.py", line 624, in arithmetic
args = ["(%s)"%self(op) for op in ex.operands()]
File "/ext/sage/sage-8.6_1804/local/lib/python2.7/site-packages/sage/symbolic/expression_conversions.py", line 207, in __call__
raise err
TypeError
```