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.


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