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Subjects · Leaving Cert Design & Communication Graphics (DCG)

Leaving Cert Design & Communication Graphics (DCG): Oblique planes & traces

How often Oblique planes & traces comes up on the Design & Communication Graphics papers, every year it was asked, and questions to try.

HL Asked on 7 of the last 9 Higher Level papers, most recently in 2025. most years

Oblique planes & traces, Higher Level(7 marks)

Quick ones on Oblique planes & traces.

(a)Where do the HT and VT of an oblique plane meet?
  1. On the X1Y1 line
  2. On the XY line
  3. Anywhere, depending on the plane
(b)To find a plane's inclination to the VP, you view along lines of the plane that are parallel to what?
  1. The normal to the plane
  2. The HP (horizontal lines)
  3. The VP (frontal lines)
(c)A line lies in a plane. Where must the line's horizontal trace be?
  1. On the plane's HT
  2. On the XY line
  3. On the plane's VT
Show the answers

(a) On the XY line

(b) The VP (frontal lines)

(c) On the plane's HT

Your turn: Higher Level questions on Oblique planes & traces.

Higher Level

Asked on 7 of the last 9 Higher Level papers, most recently in 2025. most years

Every paper, year by year

YearWhere it came up
2025A3, B2
2024A2, B1
2023A3, A4
2022B1, B3
2021Not asked
2019B3
2018Not asked
2017A4, B2
2016B1

Links open the State Examinations Commission’s paper for that year.

More Oblique planes & traces questions

Oblique planes & traces, 3 marks

For an oblique plane, what do its inclinations to the HP and to the VP add up to?

  1. Exactly 90°
  2. Less than 90°
  3. More than 90°
Show the answer

More than 90°

The sum is exactly 90° only for a plane perpendicular to the end-view plane (both traces parallel to XY). For any plane whose traces meet on XY it is more than 90°.

Oblique planes & traces, 3 marks

A plane's VT is perpendicular to XY and its HT is at 40° to XY. What is the plane?

  1. Oblique, at 40° to both
  2. Vertical, inclined at 40° to the VP
  3. Inclined at 40° to the HP, square to the VP
Show the answer

Vertical, inclined at 40° to the VP

A VT square to XY means the plane is vertical. Its plan is then a single line (the HT), and the angle that line makes with XY is the plane's true angle to the VP.

Oblique planes & traces, 3 marks

A plane's line of greatest slope falls 1 in 2. What is the plane's inclination to the HP?

  1. ≈26.6°
  2. ≈63.4°
  3. 30°
Show the answer

≈26.6°

1 in 2 means 1 unit of fall for every 2 horizontal, so tan θ = 1/2 and θ ≈ 26.6°. The line of greatest slope makes the same angle with the HP as the plane.

Other Design & Communication Graphics (DCG) topics

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