1.

If `vec(a)=(hat(i)+2hat(j)-3hat(k)) and vec(b)=(3hat(i)-hat(j)+2hat(k))` then the angle between `(vec(a)+vec(b))` and `(vec(a)-vec(b))` isA. `(pi)/(3)`B. `(pi)/(4)`C. `(pi)/(2)`D. `(2pi)/(3)`

Answer» Correct Answer - C
`(vec(a)+vec(b))=(4hat(i)+hat(j)-hat(k)) and (vec(a)-vec(b))=(-2hat(i)+3hat(j)-5hat(k))`.
`:. cos theta=((vec(a)+vec(b)).(vec(a).vec(b)))/(|vec(a)+vec(b)|.|vec(a)-vec(b)|)=(-8+3+5)/(sqrt(18)xxsqrt(38))=0rArrtheta=(pi)/(2)`


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