Given,
a=i^−j^+2k^ , a×b=2i^−k^ and a⋅b=3
Now using the formula ∣a×b∣2+∣a⋅b∣2=(∣a∣2⋅∣b∣2sin2θ+∣a∣2⋅∣b∣2cos2θ)
⇒∣a×b∣2+∣a⋅b∣2=∣a∣2⋅∣b∣2(sin2θ+cos2θ)=∣a∣2⋅∣b∣2
We get,
⇒∣2i^−k^∣2+∣3∣2=∣i^−j^+2k^∣2∣b∣2
⇒∣b∣2=65+9=614=37
Now finding ∣a−b∣=∣a∣2+∣b∣2−2∣a∣∣b∣=6+37−6=37
Now projection of b on a−b=∣a−b∣b⋅(a−b)
=∣a−b∣b⋅a−∣b∣2=373−37
=212