3D Geometry Principles

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Questions and Answers

How many straight lines are equally inclined to the three-dimensional coordinate axes?

  • 4
  • 6
  • 2
  • 8 (correct)

Given a point P with coordinates (3, 12, 4) with respect to the origin O, what are the direction cosines of OP?

  • 3, 12, 4
  • $\frac{1}{4}, \frac{1}{3}, \frac{1}{2}$
  • $\frac{3}{13}, \frac{12}{13}, \frac{4}{13}$ (correct)
  • $\frac{3}{\sqrt{13}}, \frac{1}{\sqrt{13}}, \frac{2}{\sqrt{13}}$

What is the projection of the line segment joining the points (-1, 0, 3) and (2, 5, 1) on the line whose direction ratios are 6, 2, 3?

  • $\frac{7}{22}$
  • $\frac{22}{7}$
  • $\frac{10}{7}$
  • $\frac{18}{7}$ (correct)

The projection of a line on the coordinate axes are 3, 4, and 5 respectively. What is the length of the line?

<p>$5\sqrt{2}$ (B)</p> Signup and view all the answers

If the three concurrent edges of a cube are coordinate axes, what are the direction ratios of the diagonal which joins the origin to the opposite corner?

<p>1, 1, 1 (B)</p> Signup and view all the answers

A line segment has endpoints at (2, 3, 5) and (4, 7, 1). What are the direction ratios of this line segment?

<p>(2, 4, -4) (C)</p> Signup and view all the answers

Given the direction cosines of a line are proportional to 2, -1, -2, determine the actual direction cosines.

<p>$\left(\frac{2}{3}, -\frac{1}{3}, -\frac{2}{3}\right)$ (B)</p> Signup and view all the answers

A point P has coordinates (a, a, a) in a 3D space. What angle does the line OP make with the x-axis, where O is the origin?

<p>$\arccos{\frac{1}{\sqrt{3}}}$ (D)</p> Signup and view all the answers

The vertices of a triangle are A(1, 0, 0), B(0, 1, 0), and C(0, 0, 1). What is the area of triangle ABC?

<p>$\frac{\sqrt{3}}{2}$ (A)</p> Signup and view all the answers

What is the distance between point A(1,2,3) and the line passing through points B(4,5,6) and C(7,8,9)?

<p>0 (A)</p> Signup and view all the answers

Flashcards

What is 4?

The number of straight lines equally inclined to the three-dimensional coordinate axes.

Direction Cosines of OP?

If a point P has coordinates (3, 12, 4) with respect to origin O, the direction cosines of OP.

Formula for Projection?

The projection of the line segment joining points (-1, 0, 3) and (2, 5, 1) on a line with direction ratios 6, 2, 3.

Line Length Formula?

The length of a line, given projections on coordinate axes are 3, 4, 5.

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Direction Ratios of Cube Diagonals

The direction ratios of the diagonals of a cube which joins the origin to the opposite corner, where the 3 concurrent edges are coordinate axes.

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Study Notes

  • The number of straight lines that are equally inclined to the three dimensional co-ordinate axes is 4.
  • For point P (3, 12, 4) with respect to origin O, the direction cosines of OP are 3/√13, 12/√13, 4/√13.
  • The projection of the line segment joining points (-1, 0, 3) and (2, 5, 1) on the line whose direction ratios are 6, 2, 3 is 22/7.
  • Given the projection of a line on coordinate axes is 3, 4, 5, then its length is 5√2.
  • The direction ratios of the diagonals of a cube which joins the origin to the opposite corner, when the 3 concurrent edges of the cube are coordinate axes, is 1, 1, 1.

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