If $|{\overrightarrow V _1} + {\overrightarrow V _2}|\, = \,|{\overrightarrow V _1} - {\overrightarrow V _2}|$ and ${V_2}$ is finite, then
${V_1}$ is parallel to ${V_2}$
${\overrightarrow V _1} = {\overrightarrow V _2}$
${V_1}$ and ${V_2}$ are mutually perpendicular
$|{\overrightarrow V _1}|\, = \,|{\overrightarrow V _2}|$
If $|{\overrightarrow V _1} + {\overrightarrow V _2}|\, = \,|{\overrightarrow V _1} - {\overrightarrow V _2}|$ and ${V_2}$ is finite, then
According to problem $|{\vec V_1} + {\vec V_2}|\; = \;|{\vec V_1} - {\vec V_2}|$
$⇒$ $|{\vec V_{{\rm{net}}}}|\; = \;|{\vec V'_{{\rm{net}}}}|$
So ${V_1}$ and ${V_2}$ will be mutually perpendicular.