If the point C (–1, 2) divides internally the line segment joining A (2, 5) and B in ratio 3 : 4, find the coordinates of B.
Let the coordinates of B be (α,β). It is given that AC:BC = 3:4. So, the coordinates of C are
3α+4×23+4,3β+4×53+4 = 3α+87,3β+207
but, the coordinates of C are (-1, 2)
3α+87 = -1 and 3β+207 = 2
⇒α = -5 and β = -2
Thus, the coordinates of B are (-5, -2).