Abhishek K. answered 02/12/24
Tutor
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Making calculus simple
- We are given that the point P (1,2,3) lies in the plane.
- Since a plane is defined by 3 non-collinear points, let’s find a couple more points in the plane.
- We know that the plane contains the line r(t) = (3t, 5-4t, 1-8t). So, we can find other points in the plane by substituting different values of t.
- Substituting t=0 in r(t) gives us the point P1 (0,5,1).
- Substituting t=1 in r(t) gives us the point P2 (3,1,-7).
- Note that P does not lie on the line r(t) since we cannot find a value of t such that (1,2,3) = (3t, 5-4t, 1-8t).
- Since P1 and P2 lie on r(t) and P does not, we conclude that P, P1, P2 are non-collinear and hence determine the plane.
- Let’s calculate the vector PP1 which joins points P and P1. PP1 = 0i + 5j + k - (i + 2j + 3k) = -i + 3j - 2k
- Similarly PP2 = (3i + j -7k) - (i + 2j + 3k) = 2i - j - 10k.
- PP1 and PP2 lie in the plane, hence their cross-product N must be a normal (perpendicular) to the plane. N = PP1 x PP2 = -32i - 14j - 5k
- Let X (x,y,z) be a point in the plane. Then, the vector PX joining points P and X lies in the plane and so is perpendicular to the vector N calculated above. So, the dot product PX.N = 0.
- PX = (xi + yj + zk) - (i + 2j + 3k) = (x-1)i + (y-2)j + (z-3)k
- Setting PX.N =0 gives us -32(x-1) - 14(y-2) - 5(z-3) = 0 which after some rearranging becomes 32x + 14y + 5z = 75.
- So, the equation of the plane is 32x + 14y + 5z = 75.