C = ...;
M = ...;
n = ...;
Bond_price = ...;
fun=@(i)C*(1./(1+i)-1./(1+i).^(n+1))./(1-1./(1+i)) + M./(1+i).^n - Bond_price;
i0 = 0.2;
sol_i = fzero(fun,i0)
sol_i is equal to the i in your equation if you give meaningful values to C, M, n and Bond_Price.
Hint for a derivation: Geometric series.
Best wishes
Torsten.
