Unit vector u^=xi^+yj^+zk^
p1=21i^+21k^,p2=21j^+21k^
p3=21i^+21j^
Now angle between u^ and p1=2π
u^⋅p1=0⇒2x+2z=0
⇒x+z=0…(i)
Angle between u^ and p2=3π
u^⋅p2=∣u^∣⋅∣p2∣cos3π
u^⋅p2=2y+2z=21…(ii)
Angle between u^ and p3=32π
u^⋅p3=∣u^∣⋅∣p3∣cos32π
⇒2x+2y=2−1⇒x+y=2−1…(iii)
from equation (i), (ii) and (iii) we get
x=2−1,y=0,z=21
Thus u^−v=2−1i^+21k^−21i^−21j^−21k^
⇒u^−v=2−2i^−21j^
∴∣u^−v∣2=(24+21)2=25