  Let $p$ be a prime number with $p>3$, $p\equiv 3\pmod{4}$ and let $n$ be a
positive integer. In this paper, we prove that the Diophantine equation
$(5pn^{2}-1)^{x}+(p(p-5)n^{2}+1)^{y}=(pn)^{z}$ has only the positive integer
solution $(x,y,z)=(1,1,2)$ where $pn \equiv \pm1 \pmod 5$. As an another
result, we show that the Diophantine equation
$(35n^{2}-1)^{x}+(14n^{2}+1)^{y}=(7n)^{z}$ has only the positive integer
solution $(x,y,z)=(1,1,2)$ where $n\equiv \pm 3% \pmod{5}$ or $5\mid n$. On the
proofs, we use the properties of Jacobi symbol and Baker's method.
