Given a×c=b.
Taking the dot product with c on both sides:
(a×c)⋅c=b⋅c
Since the scalar triple product with two identical vectors is zero, we get:
b⋅c=0
We need to find the value of c⋅(a−2b). Expanding the dot product:
c⋅(a−2b)=c⋅a−2(c⋅b)
It is given that a⋅c=3. Substituting the values:
c⋅(a−2b)=3−2(0)=3
Answer: 3