I am unable to isolate the variable $z$ in the following equation and cannot solve for it. Is it even possible? If so how?
$$B = \frac{R}{z} (1-(1+z)^{-L})$$
I want to, in general, be able to fine the interest rate that corresponds to an annuity. Whoever changed my equation in LaTex forgot to put the -L as an exponent and made it less easy to interpet by simplyfing. L = maturity, B = present value of the annuity, z = interest-rate/period, R = payment/period.
Actually the present value $B$, for an annuity of $L$ years with interest rate $z$ and payments $R$ is
$$ B=R\,a_{\overline{L}|z}=R\frac{1-(1+z)^{-L}}{z} $$ and it can only be solved numerically to find $z$.