Factor out r³ in the first equation
Multiply both sides of second equation by (1-r).
[Note that r cannot equal to 1 for that would make
the denominator of the original second equation 0.

  

Write the first equation as



Use the zero-factor principle:

 

Now we must find corresponding values
for "a":

Substitute a=0 in the second equation


 




But we must disregard that value since it
causes the denominator in the original second
equation to become 0.  Therefore we must
also disregard a=0.

Substitute r=0 in the second equation


 


So one solution is (a,r) = (93,0)

Substitute  in the second equation


 




Although that satisfies the second equation, we must check to
see if it satisfies the first equation as well:








The fractional powers of 8 are irrational, so none
of those factors can equal 0, so the equation cannot be true
so  does not produce a solution.
However we could not have known this without substituting
in the first equation.

There is but one solution: (a,r) = (93,0)

Edwin