Since,

Let &

Angle between is and angle between is

By vector addition method;

we have:

=2(1+cos θ)

=2(1-cos θ)

So,

Now in the parallelogram:

Area of parallelogram= (product of two sides and the sine of angle between them)

i.e. (1)

Also area of parallelogram= sum of area of all four triangle

And area of each triangle =

So, Area = 2

Since are supplementary

A= 4= (2)

From (1) &(2) we get: