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Angle between the vectors vec(a)=-hat(i)...

Angle between the vectors `vec(a)=-hat(i)+2hat(j)+hat(k)` and `vec(b)=xhat(i)+hat(j)+(x+1)hat(k)`

A

is obtuse angle

B

is acute angle

C

is `90^(@)`

D

depends on x

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Verified by Experts

The correct Answer is:
B, D
Angle between `vec(a)` and `vec(b)`,
`cos theta=(vec(a).vec(b))/(ab)=(-x+2+x+1)/(sqrt(1+4+1)sqrt(x^(2)+1^(2)+(x+1)^(2)))`
`=(3)/sqrt(6[x^(2)+1+(x+1)^(2)]) gt 0`
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