1.

सदिश `vecr_(1)=(4 hati-2hatj+5hatk)` तथा `vecr_(2)=(3hati+4hatj+5hatk)` के बीच का कोण ज्ञात कीजिए।

Answer» यदि `vecr_(1)` तथा `vecr_(2)` के बीच का कोण `theta` है। तब
`cos theta =(vecr_(1)*vecr_(2))/(|vecr_(1)|vecr_(2)|)`
`=((4hati-3hatk+5hatk)*(3hati+4hatj+5hatk))/({sqrt((4)^(2)+(-3)^(2)+(5)^(2))}{sqrt((3)^(2)+(4)^(2)+(5)^(2))})`
`=(12-12+25)/({sqrt(16+9+25)}{sqrt(+16+25)})`
`=(25)/(sqrt(50)xxsqrt(50))=(25)/(50)=(1)/(2)`
`:. cos theta=(1)/(2)`
`theta= "cos"^(-)(1)/(2)=(pi)/(3)`


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