Mathematics problems in senior two (space vector) Let a, B, C, d be four non coplanar points in space, and satisfy (vector AB) * (vector AC) = 0, (vector AB) * (vector AD) = 0, (vector AC) * (vector AD) = 0 Then triangle BCD is () triangle? A. Obtuse angle B. Right angle C. Acute angle D. Equilateral Why?

Mathematics problems in senior two (space vector) Let a, B, C, d be four non coplanar points in space, and satisfy (vector AB) * (vector AC) = 0, (vector AB) * (vector AD) = 0, (vector AC) * (vector AD) = 0 Then triangle BCD is () triangle? A. Obtuse angle B. Right angle C. Acute angle D. Equilateral Why?

Let C be an acute triangle. The proof is as follows: if the vectors AB, AC and AD are perpendicular to each other, a, B, C and D are four non coplanar points in space, then the plane rectangular coordinate system can be established with a as the origin, and let AB = (x, 0,0), AC = (0, y, 0), ad = (0,0, z), then the vector DB = Da + AB = (x, 0, - z), DC = Da + AC = (x, y