(
1
+
i
)
⋅
(
1
+
i
)
=
1
+
2
i
+
i
2
=
1
+
2
i
−
1
=
2
i
(
1
+
i
)
⋅
(
1
+
i
)
=
1
+
2
i
+
i
2
=
1
+
2
i
−
1
=
2
i