यदि सदिश `veA=A_(x)hati+A_(y)hatj+A_(z)hatk` तथा सदिश `vecB=B_(x)hati+B_(y)hatj+B_(z)hatk` के बीच का कोण `theta` हो तो सिद्ध कीजिए कि
`cos theta=(A_(x)B_(x)+A_(y)B_(y)+A_(z)B_(z))/(sqrt(A_(x)^(2)+A_(y)^(2)+A_(z)^(2))sqrt(B_(x)^(2)+B_(y)^(2)+B_(z)^(2)))`