What is the angle between
Vector is perpendicular to the plane containing
is the resultant of
therefore lies in the plane containing
∴ Angle between and is
Alternatively:
If , the do you think that A is necessarily equal to C?
Here,
Let the angle between be and that between be .
∴
and
Therefore,
Now,
and then
Thus, A is not necessarily equal to C.
If diagonals of a parallelogram are then find the area of the parallelogram.
Let the sides of the parallelogram be whose diagonals are
L.H.S. =
= R.H.S.
Hence, proved.