Question

the vector product of two vector A nd b is zero .the scaler product of A nd (a+b)will be

Answer 1

Whenever the dot product of two vectors is Zero...... then the two vectors is perpendicular to each other. Now......coming to your question........ ( a + b ) vector will always be in the plane of a and b vector. For instance if they are in x, y plane, their resultant will also be in the same plane. Now dot product( scalar product) which are the same thing..... of a and b is zero. That implies that they are perpendicular to each other. Now ( a + b ) vector is in the same plane as a and b..... therefore their dot product( scalar product ) will be a third vector perpendicular to their plane, which in this case is x, y plane. 
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