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JEE Advanced 2013 · Three Dimensional Geometry

Consider the lines L1:x−12=y−1=z+31, L2:x−41=y+31=z+32L_1 : \frac{x-1}{2} = \frac{y}{-1} = \frac{z+3}{1},\ L_2 : \frac{x-4}{1} = \frac{y+3}{1} = \frac{z+3}{2} and the planes P1:7x+y+2z=3, P2:3x+5y−6z=4P_1 : 7x + y + 2z = 3,\ P_2 : 3x + 5y - 6z = 4. Let ax+by+cz=dax + by + cz = d be the equation of the plane passing through the point of intersection of lines L1L_1 and L2L_2, and perpendicular to planes P1P_1 and P2P_2. Match List I with List II and select the correct answer using the code given below the lists : | List I | List II | | --- | --- | | (P) a=a = | (1) 1313 | | (Q) b=b = | (2) −3-3 | | (R) c=c = | (3) 11 | | (S) d=d = | (4) −2-2 |

Answer: A. (P)→(3),(Q)→(2),(R)→(4),(S)→(1)(P) \to (3), (Q) \to (2), (R) \to (4), (S) \to (1)

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Consider the lines L₁ : (x-1)/2 = y/(-1) = (z+3)/1, L₂ : (x-4)/1 = (y+3)/1 = (z+3)/2 and the planes P₁ : 7x + y + 2z = 3, P₂ : 3x + 5y - 6z = 4. Let ax + by + cz = d be the equation of the plane passing through the point of intersection of lines L₁ and L₂, and perpendicular to planes P₁ and P₂. Match List I with List II and select the correct answer using the code given below the lists : | List I | List II | | --- | --- | | (P) a = | (1) 13 | | (Q) b = | (2)

L1:x−12=y−1=z+31,L2:x−41=y+31=z+32L_1 : \frac{x-1}{2} = \frac{y}{-1} = \frac{z+3}{1}, \quad L_2 : \frac{x-4}{1} = \frac{y+3}{1} = \frac{z+3}{2}

P1:7x+y+2z=3,P2:3x+5y−6z=4P_1 : 7x+y+2z=3, \quad P_2 : 3x+5y-6z=4

To find: plane ax+by+cz=d⊥P1, P2 through L1∩L2\text{To find: plane } ax+by+cz=d \perp P_1,\ P_2 \text{ through } L_1 \cap L_2

Match a, b, c, d with List II\text{Match } a,\ b,\ c,\ d \text{ with List II}

L1:A(1,0,−3),d⃗1=(2,−1,1)L_1: A(1,0,-3), \quad \vec{d}_1 = (2,-1,1)

L2:B(4,−3,−3),d⃗2=(1,1,2)L_2: B(4,-3,-3), \quad \vec{d}_2 = (1,1,2)

L1:(1+2s, −s, −3+s)L_1: (1+2s,\ -s,\ -3+s) L2:(4+t, −3+t, −3+2t)L_2: (4+t,\ -3+t,\ -3+2t)

2s−t=3,s+t=3,s=2t2s - t = 3, \quad s + t = 3, \quad s = 2t

s=2,t=1s = 2, \qquad t = 1

L1(2)=(1+4, −2, −3+2)=(5,−2,−1)L_1(2) = (1+4,\ -2,\ -3+2) = (5,-2,-1)

L2(1)=(4+1, −3+1, −3+2)=(5,−2,−1)L_2(1) = (4+1,\ -3+1,\ -3+2) = (5,-2,-1)

n⃗1=(7,1,2),n⃗2=(3,5,−6)\vec{n}_1 = (7,1,2), \qquad \vec{n}_2 = (3,5,-6)

n⃗=n⃗1×n⃗2\vec{n} = \vec{n}_1 \times \vec{n}_2

n⃗ = î ĵ k̂ 7 1 2 3 5 -6

=(−6−10)i^−(−42−6)j^+(35−3)k^= (-6-10)\hat{i} - (-42-6)\hat{j} + (35-3)\hat{k}

n⃗=−16i^+48j^+32k^\vec{n} = -16\hat{i} + 48\hat{j} + 32\hat{k}

n⃗∝(−16,48,32)∝(−1,3,2)∝(1,−3,−2)\vec{n} \propto (-16,48,32) \propto (-1,3,2) \propto (1,-3,-2)

1(x−5)−3(y+2)−2(z+1)=01(x-5) - 3(y+2) - 2(z+1) = 0

x−3y−2z=13x - 3y - 2z = 13

ax+by+cz=d≡x−3y−2z=13ax+by+cz=d \equiv x-3y-2z=13

a=1,b=−3,c=−2,d=13a=1, \quad b=-3, \quad c=-2, \quad d=13

a=1→(3),b=−3→(2)a=1 \to (3), \quad b=-3 \to (2)

c=−2→(4),d=13→(1)c=-2 \to (4), \quad d=13 \to (1)

(P)→(3), (Q)→(2), (R)→(4), (S)→(1) ⇒ option (1)(P)\to(3),\ (Q)\to(2),\ (R)\to(4),\ (S)\to(1) \ \Rightarrow \ \text{option (1)}

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