Find the value of x such that the points A(3, 2, 1), B(4, x, 5), C(4, 2, −2) and D(6, 5, −1) are coplanar.
Find the value of x such that the points A(3, 2, 1), B(4, x, 5), C(4, 2, −2) and D(6, 5, −1) are coplanar.
- A. 5
- B. 3
- C. 1
- D. −1
Answer: A) 5
Explanation: Vectors AB = î + (x−2)ĵ + 4k̂, AC = î + 0ĵ − 3k̂, AD = 3î + 3ĵ − 2k̂. Coplanar means [AB AC AD] = 0. Det: 1(0 − (−9)) − (x−2)(−2 − (−9)) + 4(3 − 0) = 0. 9 − 7(x−2) + 12 = 0. 21 = 7(x−2). x−2 = 3 → x = 5.
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