Question #251900

You are given the line l:r=(1+2λ,1λ,3λ)l:\mathbf{r}=(1+2\lambda,-1-\lambda,3\lambda) , where λ\lambda is a parameter.

Which of the following statements are true?




  1. The point (3,-2,3) lies on the line ll
  2. The vector (2,−1,3) is parallel to the line.
  3. Line ll is perpendicular to the line r=(2t,2t,1+3t)\mathbf{r}=(2t, 2-t,-1+3t) , where tt is a parameter.
  4. The equation of a plane containing line ll and also passing through the point (0,2,1)(0,2,−1) is 8x+y5z=78x+y-5z=7 .
  5. The vector (2,1,3)(2,−1,3) is perpendicular to the line ll .
1
Expert's answer
2021-10-18T07:14:55-0400

1.If the point (3, -2, 3) lies on the line l:r=(1+2λ,1λ,3λ)l: r=(1+2\lambda,-1-\lambda,3\lambda), then (1+2λ=3)(1λ=2)(3λ=3)(1+2\lambda=3)\land(-1-\lambda=-2)\land(3\lambda =3)

All three conditions is true when λ=1\lambda= 1, so the point lies on the line ll when λ=1\lambda = 1

2.If the vector (2, -1, 3) is parallel to the line, then tR:t(a,b,c)=(2,1,3)\exist t\in R:t*(a, b, c) = (2, -1, 3), where a, b, c - coefficients before λ\lambda for every coordinate

In our case: a = 2, b = -1, c = 3. So If the vector (2, -1, 3) is parallel to the line, then tR:t(2,1,3)=(2,1,3)\exist t\in R:t*(2, -1, 3) = (2, -1, 3). We have equility when t = 1, so vector (2, -1, 3) is parallel to the line

3.If two lines are perpendicular, the a1a2+b1b2+c1c2=0a{\scriptscriptstyle 1}*a{\scriptscriptstyle 2}+b{\scriptscriptstyle 1}*b{\scriptscriptstyle 2}+c{\scriptscriptstyle 1}*c{\scriptscriptstyle 2} = 0, where a1,b1,c1a{\scriptscriptstyle 1},b{\scriptscriptstyle 1},c{\scriptscriptstyle 1} and a2,b2,c2a{\scriptscriptstyle 2}, b{\scriptscriptstyle 2}, c{\scriptscriptstyle 2} are coefficients before parameters for every coordinate for first and second line

In our case: a1a2+b1b2+c1c2=22+(1)(1)+33=140a{\scriptscriptstyle 1}*a{\scriptscriptstyle 2}+b{\scriptscriptstyle 1}*b{\scriptscriptstyle 2}+c{\scriptscriptstyle 1}*c{\scriptscriptstyle 2} = 2*2 + (-1)*(-1)+3*3 = 14 \not = 0\to lines aren't perpendicular

4.Firstly we find two points that belong to the line l

M1=(1,1,0)M{\scriptscriptstyle 1} = (1, -1, 0), when λ=0\lambda = 0

M2=(3,2,3)M{\scriptscriptstyle 2} = (3, -2, 3), when λ=1\lambda =1

M3=(0,2,1)M{\scriptscriptstyle 3} = (0, 2, -1)

Now we have to find the equation of the plane that contains 3 points

det(x1y+1z312+13012+11)\begin{pmatrix} x-1 & y+1 & z \\ 3-1 & -2+1&3 \\ 0-1&2+1&-1 \end{pmatrix} = (x-1)*(-2+1)*(-1)+(y+1)*3*(-1)+z*(3-1)*(2+1)-(-1)*(-2+1)*z-(2+1)*3*(x--1)-(-1)*(3-1)(y+1) = x-1-3y-3+6z-z-9x+9+2y+2 = -8x - y +5z +7 = 0

The equation of the plane is 8xy+5z+7=08x+y5z+7-8x - y +5z +7 = 0 \to 8x+y-5z+7 \to The statement is true

5.In the second statement we found out that that vector is parallel to the line, so it's not perpendicular


So, the statements 1, 2, 4 are true


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