If veca=xhati+ (x-1)hatj+hatkandvecb= (...

If `veca=xhati+ (x-1)hatj+hatkandvecb= (x+1)hati+hatjahatk` make an acute angle `AAx inR,` then find the values of a.

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`veca.vecb= (xhati+(x-1)hatj+hatk).((x+1)hati+hatj+ahatk)`
`x(x+1)x-1+a`
we must have `veca.vecbgt0AAx inR`
`Rightarrowx^(2)+2x+a-1gt0AAx in R`
` Rightarrow 4-4 (a-1)gt0`
or `agt2`

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