1.
P(3,−1,2)P(3,-1,2), Q(1,2,−4)Q(1,2,-4). R,SR,S with PRPR direction ratios (4,−1,2)(4,-1,2) and QSQS direction ratios (−2,1,−2)(-2,1,-2). PRPR and QSQS intersect at TT. If TA⃗⊥PR⃗,QS⃗\vec{TA}\perp\vec{PR},\vec{QS} and ∣TA⃗∣=5|\vec{TA}|=\sqrt{5}, then ∣OA⃗∣|\vec{OA}| is