1.

The projection of the vector `vec(A)= hat(i)-2hat(j)+hat(k)` on the vector `vec(B)= 4hat(i)-4hat(j)+7hat(k)` isA. `(19)/9`B. `(38)/9`C. `8/9`D. `4/9`

Answer» Correct Answer - A
Here, `vec(A)= hat(i)-2hat(j)+hat(k)`
`vec(B)= 4hat(i)-4hat(j)+7hat(k)`
The projection of `vec(A)` on `vec(B)= A cos theta`
`A cos theta= (AB cos theta)/B= (vec(A).vec(B))/B`
`=((hat(i)-2hat(j)+hat(k)).(4hat(i)-4hat(j)+7hat(k)))/(sqrt((4)^(2)+(-4)^(2)+(7)^(2)))`
`=(4+8+7)/(sqrt(18))=(19)/9`


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