Question

Даны точки: А(2; –8; 1), В(–7; 10; –8), С(–8; 0; –10), D( –9; 8; 7). Найдите: угол между векторами AB и CD .

Answer 1

cos(<AB,CD)={AB*CD}/{iABI*ICDI}

AB={-7-2,10+8,-8-1}={-9,18,-9}

IABI=V(81+324+81)=V(486)

CD={-9+8,8-0,7+10}={-1,8,17}

ICDI=V(1+64+289)=V354

AB*CD={-9,18,-9}*{-1,8,17}=9+144-153=0

cos=0/{IABI*ICDI}=0    угол 90*