Class 7 Mathematics Ch 7 Mastery Guide: Transformations, Cartesian Plane, Translations, Reflections & Rotational Symmetry (FBISE)
Instructional Guide: Unit 07 Transformations
- Understand and use the Cartesian coordinate system (axes, origin, ordered pairs $(x, y)$, abscissa, and ordinate).
- Identify and plot points across all four quadrants and along coordinate axes.
- Connect plotted points to identify and classify 2D geometric shapes (triangles, rectangles, squares, polygons).
- Define and perform translations on points, lines, and shapes using algebraic mapping $(x, y) \to (x \pm a, y \pm b)$.
- Understand reflections and draw lines of symmetry for various geometric and real-world figures.
- Determine the order of rotational symmetry ($n$) and calculate the angle of rotation ($\theta = \frac{360^\circ}{n}$).
- Number Line: Positive numbers lie to the right/up; negative numbers lie to the left/down.
- Basic Geometry: Properties of triangles, rectangles, squares, kites, parallelograms, and regular polygons.
- Basic Arithmetic: Adding and subtracting integers on horizontal and vertical number lines.
- Ordered Pair Reversal: Confusing $(x, y)$ with $(y, x)$. Emphasize that $(5, 2)$ (5 right, 2 up) is completely different from $(2, 5)$ (2 right, 5 up).
- Points on Axes: Thinking $(0, 4)$ or $(-3, 0)$ belongs to a quadrant. Points on axes lie on the boundaries and belong to no quadrant.
- Rectangle Diagonals: Mistakenly believing diagonals of a non-square rectangle are lines of symmetry. (A rectangle only has 2 lines of symmetry through side midpoints).
- Parallelogram Symmetry: Thinking a general parallelogram has reflection lines. It has zero lines of symmetry, but rotational symmetry of order 2.
Connect transformations to video game animation (sprites moving across screens), GPS navigation maps (latitude/longitude coordinates), kaleidoscope patterns (reflections and rotations), and architectural tile mosaics.
1. The Cartesian Coordinate Plane & Ordered Pairs
Just as a street map uses names and numbers to pinpoint houses, the Cartesian Coordinate Plane allows mathematicians and scientists to pinpoint any exact location in a flat 2D space.
Core Components of the Coordinate System:
- x-axis: The horizontal number line extending infinitely left (-) and right (+).
- y-axis: The vertical number line extending infinitely down (-) and up (+), perpendicular ($90^\circ$) to the x-axis.
- Origin $O(0, 0)$: The central intersection point where both number lines cross at zero.
- Ordered Pair $(x, y)$: A pair of numbers giving the exact horizontal distance ($x$-coordinate or abscissa) and vertical distance ($y$-coordinate or ordinate).
The Four Quadrants:
| Quadrant | x-coordinate (Abscissa) | y-coordinate (Ordinate) | Sign Pattern | Example Point |
|---|---|---|---|---|
| Quadrant I (Top Right) | Positive ($x > 0$) | Positive ($y > 0$) | (+, +) | $(4, 5)$ |
| Quadrant II (Top Left) | Negative ($x < 0$) | Positive ($y > 0$) | (-, +) | $(-3, 6)$ |
| Quadrant III (Bottom Left) | Negative ($x < 0$) | Negative ($y < 0$) | (-, -) | $(-5, -2)$ |
| Quadrant IV (Bottom Right) | Positive ($x > 0$) | Negative ($y < 0$) | (+, -) | $(2, -7)$ |
| Coordinate Axes & Origin | Points on the x-axis have $y = 0$ (e.g. $(6, 0)$). Points on the y-axis have $x = 0$ (e.g. $(0, -4)$). They lie on boundaries and belong to no quadrant. | |||
2. Exercise 7.1 (100% Solved Step-by-Step)
(a) $P_1(1, 5)$ • (b) $P_2(-2, 1)$ • (c) $P_3(-2, -2)$ • (d) $P_4(2, -4)$ • (e) $P_5(6, -2)$ • (f) $P_6(3, 3)$ • (g) $P_7(5, 0)$ • (h) $P_8(5, 2)$ • (i) $P_9(0, -4)$ • (j) $P_{10}(-6, -2)$
• (a) $P_1(1, 5)$: $x = 1 > 0, y = 5 > 0 \implies$ Quadrant I
• (b) $P_2(-2, 1)$: $x = -2 < 0, y = 1 > 0 \implies$ Quadrant II
• (c) $P_3(-2, -2)$: $x = -2 < 0, y = -2 < 0 \implies$ Quadrant III
• (d) $P_4(2, -4)$: $x = 2 > 0, y = -4 < 0 \implies$ Quadrant IV
• (e) $P_5(6, -2)$: $x = 6 > 0, y = -2 < 0 \implies$ Quadrant IV
• (f) $P_6(3, 3)$: $x = 3 > 0, y = 3 > 0 \implies$ Quadrant I
• (g) $P_7(5, 0)$: $y = 0, x = 5 \implies$ On the positive x-axis (not in any quadrant)
• (h) $P_8(5, 2)$: $x = 5 > 0, y = 2 > 0 \implies$ Quadrant I
• (i) $P_9(0, -4)$: $x = 0, y = -4 \implies$ On the negative y-axis (not in any quadrant)
• (j) $P_{10}(-6, -2)$: $x = -6 < 0, y = -2 < 0 \implies$ Quadrant III
Graph (a):
• $A = (-2, 4)$ (2 units left, 4 units up)
• $B = (3, 3)$ (3 units right, 3 units up)
• $C = (4, 2)$ (4 units right, 2 units up)
• $D = (3, -1)$ (3 units right, 1 unit down)
• $E = (4, -3)$ (4 units right, 3 units down)
• $F = (3, -4)$ (3 units right, 4 units down)
• $G = (-2, -4)$ (2 units left, 4 units down)
• $H = (0, -3)$ (On y-axis at -3)
• $I = (-2, 0)$ (On x-axis at -2)
Graph (b):
• $S = (-3, 4)$ • $W = (-2, 0)$ • $U = (-2, -2)$ • $T = (0, -3)$ • $R = (2, -4)$ • $V = (2, -2)$ • $X = (3, 0)$ • $Y = (1, 2)$ • $Z = (2, 4)$
• (a) $A(2, 4) \to$ Quadrant I (+, +)
• (b) $B(-6, 2) \to$ Quadrant II (-, +)
• (c) $D(-6, -7) \to$ Quadrant III (-, -)
• (d) $F(-4, -5) \to$ Quadrant III (-, -)
• (e) $P(1, 3) \to$ Quadrant I (+, +)
• (f) $K(4, -3) \to$ Quadrant IV (+, -)
• (g) $R(0, 7) \to$ On positive y-axis (not in any quadrant)
• (h) $H(6, -2) \to$ Quadrant IV (+, -)
• (i) $S(-5, 0) \to$ On negative x-axis (not in any quadrant)
• (j) $T(-3, 5) \to$ Quadrant II (-, +)
Answer: In an ordered pair $(x, y)$, order is essential. The first value is the horizontal position along the x-axis and the second value is the vertical position along the y-axis. The point $(5, 2)$ is located $5$ units right and $2$ units up, while $(2, 5)$ is located $2$ units right and $5$ units up. Because they locate two entirely different physical positions on the Cartesian plane, $(5, 2) \ne (2, 5)$.
(b) Under what circumstances is a point not in any quadrant?
Answer: A point is not in any quadrant when at least one of its coordinates is zero ($x = 0$ or $y = 0$). If $y = 0$, the point lies on the x-axis; if $x = 0$, the point lies on the y-axis; if both $x = 0$ and $y = 0$, it is the origin $(0, 0)$. The axes are the boundary lines dividing the plane and do not belong to any quadrant.
• (b) $(-3, -2), (4, -1), (-2, 4)$: 3 non-collinear points form a Triangle.
• (c) $(1, 2), (1, -2), (5, 2), (5, -2)$: Vertical side length $= |2 - (-2)| = 4$ units; Horizontal side length $= |5 - 1| = 4$ units. All sides are 4 units and perpendicular, forming a Square (Area $= 16\text{ sq units}$).
• (d) $(-4, 1), (-4, 6), (-1, 1), (-1, 6)$: Vertical length $= |6 - 1| = 5$ units; Horizontal width $= |-1 - (-4)| = 3$ units. Opposite sides are equal with $90^\circ$ angles, forming a Rectangle (Area $= 15\text{ sq units}$).
• (e) $(0, -6), (2, -2), (5, -4)$: Joining the 3 points forms a Triangle.
3. Geometric Transformations: Translations
A transformation is an operation that maps an original geometric figure (called the pre-image) onto a new figure (called the image). A translation (or slide) moves every point of a figure by the same distance in a specified direction without rotating, flipping, or resizing it.
Coordinate Translation Rules:
| Shift $a$ units Right: | $(x, y) \to (x + a, y)$ |
| Shift $a$ units Left: | $(x, y) \to (x - a, y)$ |
| Shift $b$ units Up: | $(x, y) \to (x, y + b)$ |
| Shift $b$ units Down: | $(x, y) \to (x, y - b)$ |
| Combined Translation: | $(x, y) \to (x \pm a, y \pm b)$ |
Key Property: Translation is a rigid isometry. The original shape and its image are strictly congruent ($\Delta ABC \cong \Delta A'B'C'$). Side lengths, angles, perimeter, and area are completely preserved.
4. Exercise 7.2 (100% Solved Step-by-Step)
• Shape 1 (Polygon): Original: $(4,0), (5,0), (6,2), (6,3), (3,3), (3,2), (4,2)$
→ (a) $(x+5, y+3): (9,3), (10,3), (11,5), (11,6), (8,6), (8,5), (9,5)$
→ (b) $(x-2, y-4): (2,-4), (3,-4), (4,-2), (4,-1), (1,-1), (1,-2), (2,-2)$
• Shape 2 (Trapezium): Original: $(-3,2), (-2,4), (-5,6), (-6,4)$
→ (a) $(x+5, y+3): (2,5), (3,7), (0,9), (-1,7)$
→ (b) $(x-2, y-4): (-5,-2), (-4,0), (-7,2), (-8,0)$
• Shape 3 (Triangle): Original: $(2,-1), (1,2), (-2,0)$
→ (a) $(x+5, y+3): (7,2), (6,5), (3,3)$
→ (b) $(x-2, y-4): (0,-5), (-1,-2), (-4,-4)$
• Shape 4 (Square): Original: $(2,-2), (0,-2), (0,-4), (2,-4)$
→ (a) $(x+5, y+3): (7,1), (5,1), (5,-1), (7,-1)$
→ (b) $(x-2, y-4): (0,-6), (-2,-6), (-2,-8), (0,-8)$
$(4+3, -5+4) = (7, -1)$; $(-2+3, 0+4) = (1, 4)$; $(-6+3, -1+4) = (-3, 3)$; $(0+3, -4+4) = (3, 0)$; $(-3+3, -8+4) = (0, -4)$
• (b) 0 units right, 4 units down $(x, y-4)$:
$(4, -9), (-2, -4), (-6, -5), (0, -8), (-3, -12)$
• (c) 1 unit left, 0 units up $(x-1, y)$:
$(3, -5), (-3, 0), (-7, -1), (-1, -4), (-4, -8)$
• (d) 5 units left, 3 units down $(x-5, y-3)$:
$(-1, -8), (-7, -3), (-11, -4), (-5, -7), (-8, -11)$
(b) Vertices of image:
• $A'(1+3, 1) = A'(4, 1)$
• $B'(5+3, 1) = B'(8, 1)$
• $C'(5+3, 5) = C'(8, 5)$
• $D'(1+3, 5) = D'(4, 5)$
(ii) Translation 0 units left and 3 units down $(x, y - 3)$:
• $A'(-10, -10 - 3) = A'(-10, -13)$
• $B'(10, -10 - 3) = B'(10, -13)$
• $C'(10, 10 - 3) = C'(10, 7)$
• $D'(-10, 10 - 3) = D'(-10, 7)$
• $A'(0, -2 + 5) = A'(0, 3)$
• $B'(2, -2 + 5) = B'(2, 3)$
• $C'(2, -4 + 5) = C'(2, 1)$
• $D'(0, -4 + 5) = D'(0, 1)$
(ii) Area of rectangle:
$\text{Length} = |2 - 0| = 2\text{ units}$, $\text{Width} = |-2 - (-4)| = 2\text{ units}$.
$\text{Area} = \text{Length} \times \text{Width} = 2 \times 2 = 4\text{ square units}$.
5. Reflections & Line of Symmetry
A reflection is a flip of a figure across a mirror line called the line of symmetry (or line of reflection). A figure has reflective symmetry (line symmetry) if it can be folded along a straight line such that both halves match exactly.
Summary of Lines of Symmetry for Standard Figures:
| Geometric Shape | Number of Lines of Symmetry | Description of Symmetry Lines |
|---|---|---|
| Equilateral Triangle | 3 | From each vertex perpendicular to the opposite midpoint |
| Isosceles Triangle | 1 | Vertical line through apex to base midpoint |
| Scalene Triangle | 0 | No matching sides or angles |
| Square | 4 | 2 joining opposite midpoints + 2 along diagonals |
| Rectangle (non-square) | 2 | 1 horizontal + 1 vertical through side midpoints (diagonals are NOT symmetry lines) |
| Rhombus | 2 | Along both perpendicular diagonals |
| Parallelogram (general) | 0 | No reflection lines (cannot be folded onto itself) |
| Regular Pentagon | 5 | From each vertex to opposite side midpoint |
| Regular Hexagon | 6 | 3 joining opposite vertices + 3 joining opposite midpoints |
| Circle | Infinite ($\infty$) | Every straight line passing through the center (diameter) is a symmetry line |
6. Rotations & Rotational Symmetry
A rotation is a circular turning motion of a figure around a fixed central point called the centre of rotation. It can turn in a clockwise or anticlockwise direction.
The number of times a figure matches its starting appearance during one complete $360^\circ$ rotation about its centre.
The smallest positive angle required to turn the shape onto itself:
$\text{Angle of Rotation} = \frac{360^\circ}{\text{Order } (n)}$
7. Exercise 7.3 (100% Solved Step-by-Step)
• (ii) Isosceles Trapezium: 1 line of symmetry (vertical line through the midpoints of the parallel top and bottom sides). (If general trapezium: 0 lines).
• (iii) Symmetrical Rabbit: 1 line of symmetry (vertical line down the middle).
• (iv) Kite: 1 line of symmetry (along the main diagonal).
• (v) Arched Window / Tomb Shape: 1 line of symmetry (vertical line down the middle).
| Figure | Order of Rotational Symmetry ($n$) | Angle of Rotation ($\theta = 360^\circ/n$) |
|---|---|---|
| (i) Rectangle | 2 | $360^\circ / 2 = \mathbf{180^\circ}$ |
| (ii) Regular Pentagon | 5 | $360^\circ / 5 = \mathbf{72^\circ}$ |
| (iii) Circle | Infinite ($\infty$) | Any angle / Infinitely small |
| (iv) 5-pointed Star | 5 | $360^\circ / 5 = \mathbf{72^\circ}$ |
| (v) Regular Hexagon | 6 | $360^\circ / 6 = \mathbf{60^\circ}$ |
$\text{Time} = 2 \times 60 \text{ min} \times 60 \text{ sec} = 7,200 \text{ seconds}$.
Step 2: Multiply by drawing frame rate:
$\text{Total Drawings} = 7,200 \times 24 = \mathbf{172,800 \text{ drawings}}$.
8. Review Exercise 7 (100% Solved Master Guide)
Q1: Multiple Choice Questions (MCQs):
Correct: (a) x-axis ($y = 0$).
Correct: (c) third quadrant (-, -).
Correct: (b) second quadrant (-, +).
Correct: (a) 0.
Correct: (b) $(-x, -y)$.
Correct: (c) $(-2, 0)$ ($y = -3 + 3 = 0$).
Correct: (a) $(-3, -5)$.
Correct: (b) $(x - h, y + k)$.
Correct: (d) $(x + h, y - k)$.
Correct: (c) $(-2, y + 1)$.
Correct: (d) $(x - 2, 1)$.
Q2 to Q10 Detailed Solutions:
- $BCDB$ forms a Right-Angled Triangle.
- $ACBA$ forms a Triangle.
- $ABEFGA$ forms a Polygon.
• Q4 (Line Segment Translation): $A(0, -1)$ and $B(0, 1)$ translated 3 left and 4 up $(x-3, y+4)$:
$A' = (0 - 3, -1 + 4) = \mathbf{(-3, 3)}$; $B' = (0 - 3, 1 + 4) = \mathbf{(-3, 5)}$.
• Q5 (Translation Rules):
(a) 0 right, 1 down $\to \mathbf{(x, y - 1)}$
(b) 1 left, 0 up $\to \mathbf{(x - 1, y)}$
(c) $h$ right, $k$ down $\to \mathbf{(x + h, y - k)}$
(d) $h$ left, $k$ down $\to \mathbf{(x - h, y - k)}$
• Q6 (Geometric Figures Identification):
(i) $(-3, -2), (-3, 3), (4, 3), (4, -2) \to$ Rectangle (Width 7, Height 5).
(ii) $(4, -1), (4, 1), (0, 1), (0, -1), (4, -2) \to$ Pentagon / Polygon.
(iii) $(0, 6), (4, 3), (0, 1) \to$ Isosceles Triangle.
• Q7 (School Coordinates): 3 units left and 4 units up from origin $\to \mathbf{(-3, 4)}$.
• Q8 (House & School): Ahmad's house $= \mathbf{(2, 5)}$; School $= \mathbf{(-3, -7)}$.
• Q9 (Square Quadrant): First coordinate positive ($x > 0$), second negative ($y < 0$) $\implies$ Quadrant IV (Fourth Quadrant).
• Q10 (Point Translation): 2 units right of $(-4, 2) \to (-4 + 2, 2) = \mathbf{(-2, 2)}$.
9. Chapter 7 Formula Card & Active Recall
QI: $(+, +)$ • QII: $(-, +)$
QIII: $(-, -)$ • QIV: $(+, -)$
$(x, y) \to (x \pm a, y \pm b)$
Preserves shape, size & area.
$\theta = \frac{360^\circ}{n}$
where $n$ is the order of rotation.
Lines of symmetry $= n$
Order of rotation $= n$
More Chapter Notes for Class 7 (FBISE)
MathematicsTest Your Knowledge on Chapter 7: Class 7 Mathematics Ch 7 Mastery Guide: Transformations, Cartesian Plane, Translations, Reflections & Rotational Symmetry (FBISE)
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Class 7 Mathematics - Ch 7: Transformations Chapter Mock Test
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