The vactors ` veca = 3hati -2hati + 2hatk and vecb =- hati -2hatk` are the adjacent sides of a parallelogram. Then , the acute angle between ` veca and vecb` isA. `pi//4`B. ` pi//3`C. ` 3pi//4`D. `2pi//3`

The vactors ` veca = 3hati -2hati + 2hatk and vecb =- hati -2hatk` are

1.	The vactors ` veca = 3hati -2hati + 2hatk and vecb =- hati -2hatk` are the adjacent sides of a parallelogram. Then , the acute angle between ` veca and vecb` isA. `pi//4`B. ` pi//3`C. ` 3pi//4`D. `2pi//3`
Answer» Correct Answer - A The diagonals of the parallelogram are given by ` vecalpha =veca =vecb and vecbeta = +- (veca -vecb)` i.e ` vecalpha = 2hati -2hatj and vecbeta = +- ( 4hati -2hatj +4hatk)` Let ` theta` be the angle between the diagonals. Then , ` cos theta = ( vecalpha .vecbeta)/(\|vecalpha\|\|vecbeta\|)` ` Rightarrow cos theta= 1/sqrt2 or, cos theta = - 1/sqrt2 Rightarrow theta = pi//4, or , theta = 3pi//4`

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The vactors ` veca = 3hati -2hati + 2hatk and vecb =- hati -2hatk` are the adjacent sides of a parallelogram. Then , the acute angle between ` veca and vecb` isA. `pi//4`B. ` pi//3`C. ` 3pi//4`D. `2pi//3`

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