Mathematics

Equation of a plane

Chapter: Analytical Geometry of Two & Three-Dimensions

Question 1 of 5 NDA MCQ
Consider the following for the next three (03) items that follow: The plane 6x + ky + 3z-12 = 0 where k 0 meets the coordinate axes at A, B and C respectively.
The equation of the sphere passing through the
origin and A, B, C is x2 + y2 + z2 - 2x - 3y - 4z = 0. What is the value of k?
Detailed Explanation

Explanation:

Since, B(0, 12/k, 0) lies on sphere

∴ 0 + (12/k)² + 0 + 0 − 3(12/k) − 0 = 0

⇒ (12/k)[12/k − 3] = 0

⇒ k = 4

Question 2 of 5 NDA MCQ

For the following two (02) items:

A plane P is parallel to the line having direction ratios ⟨1, 3, 2⟩ and contains the line of intersection of the planes 6x + 4y - 5z = 2 and x - 2y + 3z = 0.

What is the equation of the plane P?

Detailed Explanation

Question 3 of 5 NDA MCQ

What is the equation of the plane passing through the point (1, 1, 1) and perpendicular to the line whose direction ratio is (3, 2, 1)?

Detailed Explanation

Question 4 of 5 NDA MCQ

If p is the perpendicular distance from origin to the plane passing through (1, 0, 0), (0, 1, 0) and (0, 0, 1), then what is 3p2 equal to?

Detailed Explanation

Question 5 of 5 NDA MCQ

If < l, m, n > are the direction cosines of a normal to the plane 2x – 3y + 6z + 4 = 0, then what is the value of 49(7l2 + m2 – n2)?

Detailed Explanation

Given the circle:

x² + y² + 2x + 6y + 1 = 0

To find the centre (a, b) and radius c, rewrite the equation in the form

(x − h)² + (y − k)² = r²

Completing the square:

(x² + 2x + 1) − 1 + (y² + 6y + 9) − 9 + 1 = 0

⇒ (x + 1)² − 1 + (y + 3)² − 9 + 1 = 0

⇒ (x + 1)² + (y + 3)² − 9 = 0

⇒ (x + 1)² + (y + 3)² = 9

⇒ [x − (−1)]² + [y − (−3)]² = 3²

Therefore, the centre is (−1, −3) and the radius is 3.

∴ a = −1, b = −3, c = 3

∴ a² + b² + c²
= (−1)² + (−3)² + 3²
= 1 + 9 + 9
= 19

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