解cos
=a*b//a//b/
=（2×2+（-2）×0+（-2）×4）/√[2^2+(-2)^2+(-2)^2]√[2^2+(0)^2+(4)^2]
=-4/2√3×2√5
=-1/√15
=-√15/15
故sin
=√1-cos^2
=√1-(-√15/15）^2
=√14/15
=√210/15