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JEE Advanced 2026 · Introduction to Three Dimensional Geometry

Let P be the plane such that it contains the straight line x−12=y−33=z+21\frac{x-1}{2}=\frac{y-3}{3}=\frac{z+2}{1} and is perpendicular to the plane x+2y+3z=4x+2y+3z=4. Let P1P_{1} be the plane which passes through the point (4,2,2)(4,2,2) and is parallel to P. Then which of the following statements is (are) TRUE?

Answers: A. The equation of the plane P is 7x−5y+z=−107x-5y+z=-10 · D. The acute angle between the plane P and the plane 2x+2y+z=32x+2y+z=3 is cos⁡−1(133)\cos^{-1}\left(\frac{1}{3\sqrt{3}}\right)

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Written solution

Given: P⊃x−12=y−33=z+21\text{Given: } P \supset \dfrac{x-1}{2} = \dfrac{y-3}{3} = \dfrac{z+2}{1}

P⊥x+2y+3z=4P \perp x + 2y + 3z = 4

P1∥P, P1∋(4,2,2)P_1 \parallel P, \ P_1 \ni (4,2,2)

To find: which of the statements (1)–(4) are TRUE\text{To find: which of the statements (1)--(4) are TRUE}

1. find n⃗P1.\ \text{find } \vec{n}_P

2. equation of P2.\ \text{equation of } P

3. test each statement3.\ \text{test each statement}

d⃗=(2,3,1),A(1,3,−2)∈L\vec{d} = (2, 3, 1), \quad A(1, 3, -2) \in L

L⊂P⇒n⃗P⋅d⃗=0L \subset P \Rightarrow \vec{n}_P \cdot \vec{d} = 0

P⊥(x+2y+3z=4)⇒n⃗P⋅(1,2,3)=0P \perp (x+2y+3z=4) \Rightarrow \vec{n}_P \cdot (1,2,3) = 0

n⃗P=d⃗×(1,2,3)=(7,−5,1)\vec{n}_P = \vec{d} \times (1,2,3) = (7, -5, 1)

7(x−1)−5(y−3)+(z+2)=07(x-1) - 5(y-3) + (z+2) = 0

P: 7x−5y+z=−10⇒(1) TRUEP:\ 7x - 5y + z = -10 \Rightarrow \text{(1) TRUE}

P1: 7x−5y+z=28−10+2=20P_1:\ 7x - 5y + z = 28 - 10 + 2 = 20

d(P,P1)=∣20−(−10)∣75=3053=23d(P, P_1) = \dfrac{|20 - (-10)|}{\sqrt{75}} = \dfrac{30}{5\sqrt3} = 2\sqrt3

⇒(2) false (says 30)\Rightarrow \text{(2) false (says 30)}

dO=∣10∣75=23=233d_O = \dfrac{|10|}{\sqrt{75}} = \dfrac{2}{\sqrt3} = \dfrac{2\sqrt3}{3}

⇒(3) false\Rightarrow \text{(3) false}

cos⁡θ=∣(7,−5,1)⋅(2,2,1)∣75⋅3=5153=133\cos\theta = \dfrac{|(7,-5,1)\cdot(2,2,1)|}{\sqrt{75}\cdot 3} = \dfrac{5}{15\sqrt3} = \dfrac{1}{3\sqrt3}

⇒(4) TRUE\Rightarrow \text{(4) TRUE}

True: (1) and (4)\text{True: } (1)\ \text{and}\ (4)

(1) and (4)\boxed{(1)\ \text{and}\ (4)}

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