# Computer Graphics Questions & Answers – 2D Reflection and Shear

This set of Computer Graphics Multiple Choice Questions & Answers (MCQs) focuses on “2D Reflection and Shear”.

1. In a rotation, by how much angle is the object rotated?
a) 45 degree
b) 90 degree
c) 180 degree
d) 360 degree

Explanation: Reflection is the mirror image of the original object. It rotates the object 1890 degrees. The left side image is formed into right side and vice versa.

2. Reflection is a special case of rotation.
a) True
b) False

Explanation: Reflection is a special case of rotation of 180° about a line in xy plane passing through the origin.

3. If two pure reflections about a line passing through the origin are applied successively the result is ___________________
a) Pure rotation
b) Quarter rotation
c) Half rotation
d) True reflection

Explanation: When we apply reflection one time, it rotates the image by 180 degrees. So, if we repeat it 2 times the total reflection will be of 360 degrees.

4. What is the determinant of the pure reflection matrix?
a) 1
b) 0
c) -1
d) 2

Explanation: The pure reflection matrix is:
[T] = | 1 0 |
| 0 -1|
So, the determinant will be = (1) (-1) – (0) (0) = 0.

5. Which of the following is NOT true?
Image formed by reflection through a plane mirror is_______________
a) of same size
b) same orientation
c) virtual
d) is at same distance from the mirror

Explanation: In the image formed by reflection through a plane mirror, the right is turned into left and left is turned into right, hence changing the orientation. So the image formed by reflection through a plane mirror is not of the same orientation.
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6. Which of the following represents shearing?
a) (x, y) → (x+a, y+b)
b) (x, y) → (ax, by)
c) (x, y) → (x cos(θ)+y sin(θ), -x sin(θ)+y cos(θ))
d) (x, y) → (x+ay, y+bx)

Explanation: The first one represent translation, the second one represents scaling, third one rotation and the last one is representing shearing.

7. If a ‘3 x 3’ matrix shears in X direction, how many elements of it are ‘1’?
a) 2
b) 3
c) 6
d) 5

Explanation: The ‘3 x 3’ matrix which shears in ‘x’ direction will have total 9 elements, 3 of which are ‘1’, 5 zeroes and 1 variable in an upper triangle which is the scaling factor.

8. If a ‘3 x 3’ matrix shears in Y direction, how many elements of it are ‘0’?
a) 2
b) 3
c) 6
d) 5

Explanation: The ‘3 x 3’ matrix which shears in ‘y’ direction will have total 9 elements, 3 of which are ‘1’, 5 zeroes and 1 variable in a lower triangle which is the scaling factor.

9. Shearing is also termed as ________________
a) Selecting
b) Sorting
c) Scaling
d) Skewing

Explanation: In the case of shear only one coordinate changes its coordinates and other preserves its values, that’s why it is also called skewing.

10. Shearing and reflection are types of translation.
a) True
b) False

Explanation: Shearing and reflection are not types of translation. They are types of transformation. Even translation is also a type of transformation.

11. Which of this is compulsory for 2D reflection.
a) Reflection plane.
b) Origin
c) Reflection axis
d) Co-ordinate axis.

Explanation: Reflection axis is the axis with respect to which reflection is done. In 3D, it is reflection plane rather than reflection axis.

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