1.
a⃗,b⃗,c⃗\vec{a}, \vec{b}, \vec{c} are three vectors such that ∣a⃗∣=3|\vec{a}| = 3, ∣b⃗∣=5|\vec{b}| = 5, ∣c⃗∣=7|\vec{c}| = 7. If a⃗,b⃗,c⃗\vec{a}, \vec{b}, \vec{c} are perpendicular to the vectors b⃗+c⃗\vec{b} + \vec{c}, c⃗+a⃗\vec{c} + \vec{a}, a⃗+b⃗\vec{a} + \vec{b} respectively, then (a⃗+b⃗+c⃗)2−2=\sqrt{(\vec{a} + \vec{b} + \vec{c})^2 - 2} =