Let P ( 3 , 2 , 3 ) , Q ( 4 , 6 , 2 ) and R ( 7 , 3 , 2 ) be the vertices of ∆ PQR . Then, the angle ∠ QPR is

Let P(3,2,3),Q(4,6,2) and R(7,3,2) be the vertices of ∆PQR. Then, the angle ∠QPR is
  1. π6
  2. cos-1718
  3. cos-1118
  4. π3

Solution

Given,

⇒QP→=-i^-4j^+k^ and RP→=-4i^-j^+k^

cos∠QPR=QP→·RP→QP→RP→

⇒cos∠QPR=4+4+11+16+116+1+1

⇒cos∠QPR=918=12

⇒∠QPR=π3

Asked in: JEE Main 2024 (29 Jan Shift 2)

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