The straight line ll has equation r=i+6j−3k+s(i−2j+2k).\mathbf{r} = i + 6j - 3k + s(i - 2j + 2k). The plane pp has equation (r−3i).(2i−3j+6k)=0.(\mathbf{r} - 3i).(2i - 3j + 6k) = 0. The line ll intersects the plane pp at the point AA.

  1. (i)

    Find the position vector of AA.

  2. (ii)

    Find the acute angle between ll and pp.

  3. (iii)

    Find a vector equation for the line which lies in pp, passes through AA and is perpendicular to ll.

Work through it with AI →

It won't just hand you the answer — it asks where you're stuck.How the checker works

Worked solution

Q3(i)

1. Express the equation of the plane in the standard scalar product form $\mathbf{r} \cdot \mathbf{n} = d$.

(r−3i)⋅(2i−3j+6k)=0(\mathbf{r} - 3\mathbf{i}) \cdot (2\mathbf{i} - 3\mathbf{j} + 6\mathbf{k}) = 0
r⋅(2i−3j+6k)=3i⋅(2i−3j+6k)\mathbf{r} \cdot (2\mathbf{i} - 3\mathbf{j} + 6\mathbf{k}) = 3\mathbf{i} \cdot (2\mathbf{i} - 3\mathbf{j} + 6\mathbf{k})
r⋅(2i−3j+6k)=(3)(2)+(0)(−3)+(0)(6)=6\mathbf{r} \cdot (2\mathbf{i} - 3\mathbf{j} + 6\mathbf{k}) = (3)(2) + (0)(-3) + (0)(6) = 6

2. Substitute the equation of the line into the equation of the plane to find the parameter $s$ at the point of intersection.

Substitute r=(1+s)i+(6−2s)j+(−3+2s)k\mathbf{r} = (1+s)\mathbf{i} + (6-2s)\mathbf{j} + (-3+2s)\mathbf{k} into the plane equation:
[(1+s)i+(6−2s)j+(−3+2s)k]⋅(2i−3j+6k)=6[(1+s)\mathbf{i} + (6-2s)\mathbf{j} + (-3+2s)\mathbf{k}] \cdot (2\mathbf{i} - 3\mathbf{j} + 6\mathbf{k}) = 6
2(1+s)−3(6−2s)+6(−3+2s)=62(1+s) - 3(6-2s) + 6(-3+2s) = 6
2+2s−18+6s−18+12s=62 + 2s - 18 + 6s - 18 + 12s = 6
20s−34=620s - 34 = 6
20s=40  ⟹  s=220s = 40 \implies s = 2

3. Substitute the value of $s$ back into the line equation to obtain the position vector of point $A$.

rA=i+6j−3k+2(i−2j+2k)\mathbf{r}_A = \mathbf{i} + 6\mathbf{j} - 3\mathbf{k} + 2(\mathbf{i} - 2\mathbf{j} + 2\mathbf{k})
rA=(1+2)i+(6−4)j+(−3+4)k\mathbf{r}_A = (1+2)\mathbf{i} + (6-4)\mathbf{j} + (-3+4)\mathbf{k}
rA=3i+2j+k\mathbf{r}_A = 3\mathbf{i} + 2\mathbf{j} + \mathbf{k}

Answer

3i+2j+k3\mathbf{i} + 2\mathbf{j} + \mathbf{k}

Q3(ii)

1. Identify the direction vector of the line $l$ and the normal vector of the plane $p$.

The direction vector of line ll is d=(1−22)\mathbf{d} = \begin{pmatrix} 1 \\ -2 \\ 2 \end{pmatrix}.

The normal vector of plane pp is n=(2−36)\mathbf{n} = \begin{pmatrix} 2 \\ -3 \\ 6 \end{pmatrix}.

2. Calculate the scalar product of the direction vector and the normal vector.

d⋅n=(1−22)⋅(2−36)\mathbf{d} \cdot \mathbf{n} = \begin{pmatrix} 1 \\ -2 \\ 2 \end{pmatrix} \cdot \begin{pmatrix} 2 \\ -3 \\ 6 \end{pmatrix}
d⋅n=(1)(2)+(−2)(−3)+(2)(6)\mathbf{d} \cdot \mathbf{n} = (1)(2) + (-2)(-3) + (2)(6)
d⋅n=2+6+12=20\mathbf{d} \cdot \mathbf{n} = 2 + 6 + 12 = 20

3. Calculate the magnitudes of the direction vector and the normal vector.

∣d∣=12+(−2)2+22=1+4+4=9=3|\mathbf{d}| = \sqrt{1^2 + (-2)^2 + 2^2} = \sqrt{1 + 4 + 4} = \sqrt{9} = 3
∣n∣=22+(−3)2+62=4+9+36=49=7|\mathbf{n}| = \sqrt{2^2 + (-3)^2 + 6^2} = \sqrt{4 + 9 + 36} = \sqrt{49} = 7

4. Calculate the acute angle between the line and the plane.

Let θ\theta be the acute angle between the line ll and the plane pp.
sin⁡θ=∣d⋅n∣∣d∣∣n∣\sin \theta = \frac{|\mathbf{d} \cdot \mathbf{n}|}{|\mathbf{d}| |\mathbf{n}|}
sin⁡θ=20(3)(7)=2021\sin \theta = \frac{20}{(3)(7)} = \frac{20}{21}
θ=sin⁡−1(2021)≈72.247∘\theta = \sin^{-1}\left(\frac{20}{21}\right) \approx 72.247^\circ
θ≈72.2∘ (to 1 d.p.)\theta \approx 72.2^\circ \text{ (to 1 d.p.)}

Answer

72.2∘72.2^\circ

Q3(iii)

1. Calculate the position vector of point $A$ from part (i) as it is needed to form the line equation.

Substitute r=(16−3)+s(1−22) into p:\text{Substitute } \mathbf{r} = \begin{pmatrix} 1 \\ 6 \\ -3 \end{pmatrix} + s\begin{pmatrix} 1 \\ -2 \\ 2 \end{pmatrix} \text{ into } p:
((1+s6−2s−3+2s)−(300))⋅(2−36)=0\left( \begin{pmatrix} 1+s \\ 6-2s \\ -3+2s \end{pmatrix} - \begin{pmatrix} 3 \\ 0 \\ 0 \end{pmatrix} \right) \cdot \begin{pmatrix} 2 \\ -3 \\ 6 \end{pmatrix} = 0
(s−26−2s−3+2s)⋅(2−36)=0\begin{pmatrix} s-2 \\ 6-2s \\ -3+2s \end{pmatrix} \cdot \begin{pmatrix} 2 \\ -3 \\ 6 \end{pmatrix} = 0
2(s−2)−3(6−2s)+6(−3+2s)=02(s-2) - 3(6-2s) + 6(-3+2s) = 0
2s−4−18+6s−18+12s=0  ⟹  20s=40  ⟹  s=22s - 4 - 18 + 6s - 18 + 12s = 0 \implies 20s = 40 \implies s = 2
OA⃗=(16−3)+2(1−22)=(321)=3i+2j+k\vec{OA} = \begin{pmatrix} 1 \\ 6 \\ -3 \end{pmatrix} + 2\begin{pmatrix} 1 \\ -2 \\ 2 \end{pmatrix} = \begin{pmatrix} 3 \\ 2 \\ 1 \end{pmatrix} = 3\mathbf{i} + 2\mathbf{j} + \mathbf{k}

2. Determine the conditions for the direction vector of the new line.

Let the direction vector of the required line be d.\text{Let the direction vector of the required line be } \mathbf{d}.
Since the line lies in plane p,d is perpendicular to the normal vector of p,n=(2−36).\text{Since the line lies in plane } p, \mathbf{d} \text{ is perpendicular to the normal vector of } p, \mathbf{n} = \begin{pmatrix} 2 \\ -3 \\ 6 \end{pmatrix}.
Since the line is perpendicular to l,d is perpendicular to the direction vector of l,v=(1−22).\text{Since the line is perpendicular to } l, \mathbf{d} \text{ is perpendicular to the direction vector of } l, \mathbf{v} = \begin{pmatrix} 1 \\ -2 \\ 2 \end{pmatrix}.

3. Calculate the direction vector $\mathbf{d}$ using the vector cross product.

d=n×v=(2−36)×(1−22)\mathbf{d} = \mathbf{n} \times \mathbf{v} = \begin{pmatrix} 2 \\ -3 \\ 6 \end{pmatrix} \times \begin{pmatrix} 1 \\ -2 \\ 2 \end{pmatrix}
d=((−3)(2)−(6)(−2)(6)(1)−(2)(2)(2)(−2)−(−3)(1))\mathbf{d} = \begin{pmatrix} (-3)(2) - (6)(-2) \\ (6)(1) - (2)(2) \\ (2)(-2) - (-3)(1) \end{pmatrix}
d=(−6+126−4−4+3)=(62−1)\mathbf{d} = \begin{pmatrix} -6 + 12 \\ 6 - 4 \\ -4 + 3 \end{pmatrix} = \begin{pmatrix} 6 \\ 2 \\ -1 \end{pmatrix}

4. Formulate the final vector equation of the new line.

The line passes through A(3,2,1) and has direction (62−1).\text{The line passes through } A(3, 2, 1) \text{ and has direction } \begin{pmatrix} 6 \\ 2 \\ -1 \end{pmatrix}.
Vector equation: r=(321)+t(62−1), where t∈R\text{Vector equation: } \mathbf{r} = \begin{pmatrix} 3 \\ 2 \\ 1 \end{pmatrix} + t \begin{pmatrix} 6 \\ 2 \\ -1 \end{pmatrix}, \text{ where } t \in \mathbb{R}

Answer

r=3i+2j+k+t(6i+2j−k),  t∈R\mathbf{r} = 3\mathbf{i} + 2\mathbf{j} + \mathbf{k} + t(6\mathbf{i} + 2\mathbf{j} - \mathbf{k}), \; t \in \mathbb{R}

AI analysis — may contain mistakes.

Worked this one out on paper? Snap your steps and Gigle's AI math checker will circle the step where it went wrong.

More questions on this topic

  1. 1The lines l1l_1 and l2l_2 have equations r=(4110)+λ(1−1−6),λ∈R\mathbf{r} = \begin{pmatrix} 4 \\ 1 \\ 10 \end{pmatrix} + \lambda \begin{pmatrix} 1 \\ -1 \\ -6 \end{pmatrix}, \lambda \in \mathbb{R}…
  2. 2A drilling company plans to install a straight pipeline ABAB through a mountain. Points (x,y,z)(x, y, z) are defined relative…
  3. 3A plane Π1\Pi_1 has equation x+y+z=3x + y + z = 3. A line passes through the points PP and QQ with position vectors i+j+2k\mathbf{i} + \mathbf{j} + 2\mathbf{k}…
  4. 4The planes Π1\Pi_1 and Π2\Pi_2 have vector equations r=λ1(i+j−k)+μ1(2i−j+k)andr=λ2(i+2j+k)+μ2(3i+j−k)\mathbf{r} = \lambda_1(\mathbf{i} + \mathbf{j} - \mathbf{k}) + \mu_1(2\mathbf{i} - \mathbf{j} + \mathbf{k}) \quad \text{and} \quad \mathbf{r} = \lambda_2(\mathbf{i} + 2\mathbf{j} + \mathbf{k}) + \mu_2(3\mathbf{i} + \mathbf{j} - \mathbf{k})…
  5. 5A home interior designer is looking to design a pull-down wardrobe lift. To test his concept, the designer built a small…