Question

If the angle between A and B with magnitudes 3 and 4 units respectively with an angle 270°
between them. Then A.B is
a) 0
b) 1
c)-1
d) 12​

Answer 1

SOLUTION::

Magnitude of vector a , |a| = 3 m

Magnitude of vector b , |b| = 4 m

(a) If resultant , R = 1 unit then,

    R = √(a²+b²+a.b.cos Ф)  

    1 = √(3² + 4² + cos Ф)

    Ф = 180°

(b) If resultant , R = 5 unit then,

    R = √(a²+b²+a.b.cos Ф)  

    5 = √(3² + 4² + cos Ф)

    Ф = 90°

(c) If resultant , R = 7 unit then,

    R = √(a²+b²+a.b.cos Ф)  

    7 = √(3² + 4² + cos Ф)

    Ф = 0°

Hope it helps!