1.

Let ` vecf(t)=[t] hat i+(t-[t]) hat j+[t+1] hat k , w h e r e[dot]`denotes the greatest integer function. Then thevectors ` vecf(5/4)a n df(t),0A. parallel to each otherB. perpendicular to each otherC. inclined at `cos^(-1) 2/(sqrt7(1-t^(2))`D. inclined at `cos ^(-1) (8+t)/(9sqrt(1+t^(2)))`

Answer» Correct Answer - d
`vecf""(5/4)= [5/4] hati+ (5/4-[5/4])hatj + [5/4=1]hatk`
`hati+ (5/4-1)hatj + 2hatk`
`hati + 1/4 hatj + 2hatk`
when `0 lt t 1 ,vecf "" (t) = 0 hati + { t-0} hatj +hatk`
` hatj +hatk`
` vecf "" (5/4) .vecf"" (t) = 2+t/4`
so, `costheta= 4/(|vect+1/4hatj + 2hatk||thatj +hatk|)`
`(2+t/4)/(sqrt(1+1/16=4)sqrt(1+t^(2)))`
` ( 8 +t)/(9sqrt(1 + t^(2)))`


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