Let
b=xi^+yj^+zk^
Then,
a×b=∣i^−1xj^−1yk^1z∣
⇒a×b=−(y+z)i^+(x+z)j^+(x−y)k^
So,
−(y+z)i^+(x+z)j^+(x−y)k^=i^−j^+0k^
Hence,
y+z=−1x+z=−1x−y=0⇒x=y
Also,
a⋅b=1
⇒−x−y+z=1
⇒−2x+z=1
⇒z=2x+1
⇒−1−x=2x+1
⇒3x=−2⇒x=−32
So, y=−32;z=−31
Hence,
b=−32i^−32j^−31k^
⇒6b=−4i^−4j^−2k^
So,
a−6b=3(i^+j^+k^)