The area of the triangle whose vertices are A (1, -1, 2), B (2, 1, -1) and C (3, -1, 2) is (in area units)

AB→=i^+2j^-3k^ BC→=i^-2j^+3k^ AB→ x BC→=i^j^k^12-31-23=-6j^-4k^ ⇒AB→ x BC→=-62+-42=52 unit ⇒Area of ∆=12AB→ x BC→=13 unit