As the associative law holds, expressions such as a(bc) are equal to (ab)c.Hence there is no need to use brackets.
We know
or
(as i.i=-1)
or
...(1)
or
...(2)(pre-multiplying b/s by j)
Now,
or
(post-multiplying b/s by k)
or
or
...(3)
From(2)&(3)
...(4)
or
(substituting i=jk in 4)
or
(using 2)
or
or
...(5)
or
or
or
...(6)
We have
(equation 5)
or
(substituting j=-ik using 6)
or
or
or
...(7)
