Question #192827

Let L1 be the line in R3 with equation (x,y,z)=(1,0,2) + t(−1,3,4); t∈R and let L2 be the line that is parallel to L1 and contains the point (1,−1,3). Let V be the plane that contains both the lines L1 and L2.

(a)Find two vectors that are both parallel to the plane V but are not parallel to one another.

(b) FindavectorthatisperpendiculartotheplaneV(c) Find an equation for the plane V.(d) Find an equation for the line L3 that is perpendicular to the plane V and contains the point (1,−1,4).


1
Expert's answer
2021-05-13T18:06:53-0400

(a) Let us compose the parametric equations of the lines  L1 and L2 :

L1:{x=1ty=3tz=2+4t{L_1}:\left\{ {\begin{matrix} {x = 1 - t}\\ {y = 3t}\\ {z = 2 + 4t} \end{matrix}} \right. , L2:{x=1ty=1+3tz=3+4t{L_2}:\left\{ {\begin{matrix} {x = 1 - t}\\ {y = -1+3t}\\ {z = 3+ 4t} \end{matrix}} \right.

The direction vector of these lines will be the vector p=(1;3;4)\overrightarrow p = \left( { - 1;3;4} \right)

Since the lines are parallel to the plane V, the vector p\overrightarrow p is also parallel to the plane.

We also know that

M1(1;0;2)L1{M_1}\left( {1;0;2} \right) \in {L_1} , M2(1;1;3)L2{M_2}\left( {1; - 1;3} \right) \in {L_2}

Since the lines are parallel to the plane V, the vector M1M2=(11;10;32)=(0;1;1)\overrightarrow {{M_1}{M_2}} = \left( {1 - 1; - 1 - 0;3 - 2} \right) = \left( {0; - 1;1} \right) is also parallel to the plane.

Since the coordinates of the vectors p\overrightarrow p and M1M2\overrightarrow {{M_1}{M_2}} are disproportionate, they are not collinear.

Answer: p=(1;3;4)\overrightarrow p = \left( { - 1;3;4} \right) , M1M2=(0;1;1)\overrightarrow {{M_1}{M_2}} =\left( {0; - 1;1} \right)

(b) The vector perpendicular to the plane is found as the vector product of vectors p\overrightarrow p and M1M2\overrightarrow {{M_1}{M_2}} :

n=ijk134011=i(3+4)+j(0+1)+k(10)=(7;1;1)\overrightarrow n = \left| {\begin{matrix} {\overrightarrow i }&{\overrightarrow j }&{\overrightarrow k }\\ { - 1}&3&4\\ 0&{ - 1}&1 \end{matrix}} \right| = \overrightarrow i \left( {3 + 4} \right) + \overrightarrow j \left( {0 + 1} \right) + \overrightarrow k \left( {1 - 0} \right) = \left( {7;1;1} \right)

Answer: n=(7;1;1)\overrightarrow n = \left( {7;1;1} \right)

(с) Since V contains L2, M2(1;1;3)V{M_2}\left( {1; - 1;3} \right) \in V

Let us make an equation of V for a point M2(1;1;3){M_2}\left( {1; - 1;3} \right) and a normal vector n=(7;1;1)\overrightarrow n = \left( {7;1;1} \right) :

7(x1)+1(y+1)+1(z3)=07x+y+z9=07(x - 1) + 1(y + 1) + 1(z - 3) = 0 \Rightarrow 7x + y + z - 9 = 0

Answer: 7x+y+z9=07x + y + z - 9 = 0

(d) If  L3 is perpendicular to the plane V then L3 is parallel to n=(7;1;1)n = \left( {7;1;1} \right) .

Then

L3:x17=y+11=z41{L_3}:\frac{{x - 1}}{7} = \frac{{y + 1}}{1} = \frac{{z - 4}}{1}

Answer: L3:x17=y+11=z41{L_3}:\frac{{x - 1}}{7} = \frac{{y + 1}}{1} = \frac{{z - 4}}{1}


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