Let and be distinct positive numbers. If the vectors and are coplanar, then c is equal to :
- (A)
- (B)
- (C)
- (D)✓ Correct
Answer: (D)
Solution
The three vectors are coplanar when their scalar triple product vanishes:
Expanding along the first row, . Setting this to zero and keeping the positive root, since , gives .
Expanding along the first row, . Setting this to zero and keeping the positive root, since , gives .
JEE Main · 2021 · 25 Jul 2021 · Shift 2 · Single correct option