Find the coordinates of the point P where the line through A(3, – 4, – 5) and B(2, – 3, 1) crosses the plane passing through three points L(2, 2, 1), M(3, 0, 1) and N(4, – 1, 0). Also, find the ratio in which P divides the line segment AB.
We know that the equation passing through two point (a, b, c) and (d, e, f) is given by
the line through A(3, – 4, – 5) and B(2, – 3, 1) is
Now let us see how a point is going to be on the line
X = – k + 3, y = k – 4, z = 6k – 5
So now let a point P be the point of the intersection of a line and the plane so let the coordinates of P = (– k + 3, k – 4, 6k – 5)
Now let us find the equation of the plane passing through L(2, 2, 1), M(3, 0, 1) and N(4, – 1, 0).
The equation of the plane passing through these three points is given by the following equation.
(x – 2)2 – (y – 2)(– 1) + (z – 1)(– 3 + 4) = 0
2x – 4 + y – 2 – z + 1 = 0
2x + y – z = 5
Now point P lies on this plane so
2(3 – k) + (k – 4) – (6k – 5) = 5
6 – 2k + k – 4 – 6k + 5 = 5
– 7k = – 2
So point P is
Now we have to find the ration in which this P divides AB
Let the ratio b m:1
We know the section formula
That is if a line AB is divided by P in ratio m:1 then
Solving
We get 19m + 19 = 14m + 21
5m = – 2
So point P divides line in ration 2:5 externally since ratio is negative.