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

1. 6 π
2. cos –1 ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ 18 7
3. 3 π
4. ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ 18 1 cos 1 –

Correct answer: 3 π

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