Two forces, (4i – 5j) N and (pi + qj) N, act on a particle P of mass m kg. The resultant
of the two forces is R. Given that R acts in a direction which is parallel to the
vector (i – 2j),
(a) find the angle between R and the vector j,
(b) show that 2p + q + 3 = 0.
Given also that q = 1 and that P moves with an acceleration of magnitude 8?5 m s–2,
(c) find the value of m.
i need help in part (b) with explanation plz