JEE Main 2024 Mathematics question
Not in JEE syllabus
Let P(3, 2, 3), Q(4, 6, 2) and R(7, 3, 2) be the vertices of ΔPQR. Then the angle ∠QPR is
Answer: (C)
Solution
The direction ratios of PQ are (1, 4, −1) and of PR are (4, 1, −1). cos∠QPR = (4 + 4 + 1)/(√18 √18) = 9/18 = 1/2, so ∠QPR = π/3.