Fourth degree reciprocal equation

[branko917]

I solve good part of this equation, it all comes down to a fourth-degree reciprocal equation that must be come down to quadratic equation and final solution, i am not capable to solve any further.
Partial solving method in attachment.
Do you think that this is the right direction to the final solution.

Thanks.

[Guest]

At one point you have
[tex]3d(50\sqrt{d^2+ 1.5^2}- 1.5)[/tex] and then
[tex]150d\sqrt{d^2+ 1.5^2}- 1.5[/tex]

That is a mistake. a(b+ c)= ab+ ac. You have to muliply the "-1.5" by 3d also.