যদি $\left|\overrightarrow{A}+\overrightarrow{B}\right| =\left|\overrightarrow{A}-\overrightarrow{B}\right|$ হয়, তবে $\overrightarrow{A}$ এবং $\overrightarrow{B}$ এর মধ্যবর্তী কোণ কত? (If $\left|\overrightarrow{A}+\overrightarrow{B}\right| =\left|\overrightarrow{A}-\overrightarrow{B}\right|$ then what will angle between $\overrightarrow{A}$ and $\overrightarrow{B}$ ?)