向量a=(cos(3/2)X,sin(3/2)X),b=(cos(X/2),sin(X/2)),且X属于[0,(派/2)],求a*b及(a+b)的绝对值
问题描述:
向量a=(cos(3/2)X,sin(3/2)X),b=(cos(X/2),sin(X/2)),且X属于[0,(派/2)],求a*b及(a+b)的绝对值
答
a*b=cos(3/2)X*cos(X/2)+sin(3/2)X*sin(X/2)=cosx
|a+b|=根号(a^2+b^2+2ab)=根号(1+1+2cosx)=2cos(x/2)