Get authentic, textbook-verified solutions for DAV Class 4 Hands-On: A Book of ICT Chapter 5: LOGO-II. This guide covers the REPEAT primitive, drawing regular polygons (triangles, squares, pentagons, hexagons, octagons, decagons, circles), pen control primitives (PU, PD, PE), turtle visibility commands (HT, ST), and complete solutions for all matching and assessment activities.
Chapter Overview: The Power of REPEAT in LOGO
Key Programming Concepts in Chapter 5:
- REPEAT Command: Eliminates repetitive typing by executing a set of instructions multiple times.
- Syntax:
REPEAT <number of times> [commands to repeat] - Turn Angle Formula: The turn angle for any regular polygon is
360 / number of sides. - Pen Control Primitives: PU (Pen Up), PD (Pen Down), PE (Pen Erase).
- Turtle Visibility: HT (Hide Turtle), ST (Show Turtle).
Angle Calculation for Regular Polygons
Because the turtle makes a complete 360-degree rotation when drawing any closed geometric figure, the turning angle is calculated as follows:
| Geometric Shape | Number of Sides | Angle Calculation (360 / Sides) | Single REPEAT Command |
|---|---|---|---|
| Equilateral Triangle | 3 | 360 / 3 = 120° | REPEAT 3 [FD 100 RT 120] |
| Square | 4 | 360 / 4 = 90° | REPEAT 4 [FD 100 RT 90] |
| Regular Pentagon | 5 | 360 / 5 = 72° | REPEAT 5 [FD 80 RT 72] |
| Regular Hexagon | 6 | 360 / 6 = 60° | REPEAT 6 [FD 70 RT 60] |
| Regular Octagon | 8 | 360 / 8 = 45° | REPEAT 8 [FD 50 RT 45] |
| Regular Decagon | 10 | 360 / 10 = 36° | REPEAT 10 [FD 50 RT 36] |
| Circle | 360 | 360 / 360 = 1° | REPEAT 360 [FD 1 RT 1] |
| Semicircle | 180 | Turns 180° | REPEAT 180 [FD 1 RT 1] (or REPEAT 90 [FD 1 RT 2]) |
Predict Output of Repeat Commands (Textbook Page 75)
3. Type the following Repeat commands and draw the figure obtained in the space provided:
| LOGO Command Given | Figure Obtained | Geometric Explanation |
|---|---|---|
? REPEAT 360 [FD 1 RT 1] | Full Smooth Circle | Moves 1 step forward and turns 1 degree right, repeated 360 times to make a complete 360° circular path. |
? REPEAT 180 [FD 1 RT 2] | Circle (Fast Render) | Moves 1 step and turns 2 degrees right, repeated 180 times (180 × 2 = 360°), drawing a full circle in half the execution steps. |
? REPEAT 90 [FD 1 RT 4] | Small Circle / Arc | Moves 1 step and turns 4 degrees right, repeated 90 times (90 × 4 = 360°), drawing a tighter circle. |
4. Match the following REPEAT commands with the designs (Textbook Page 75):
| Command Set | Output Design Pattern |
|---|---|
(i) REPEAT 90 [FD 1 RT 4]REPEAT 90 [FD 1 LT 4] | Two Adjacent Circles / Figure-8 Loops (Touching at perimeter) |
(ii) REPEAT 360 [FD 1 RT 1]REPEAT 180 [FD 1 RT 2]REPEAT 90 [FD 1 RT 4] | Concentric Circles of Different Sizes sharing the base tangency |
(iii) REPEAT 60 [FD 1 LT 6]PU RT 90 FD 50 LT 90 PDREPEAT 60 [FD 1 RT 6] | Concentric Displaced Arcs / Circular Rings with offset distance |
Assessment Activity (Textbook Page 76)
1. Write the command to draw a 10 sided figure:
Answer: REPEAT 10 [FD 50 RT 36]
(Reason: A 10-sided polygon has an exterior turn angle of 360 ÷ 10 = 36 degrees.)
2. Draw the following designs with Repeat command:
Commands for Complex Repeating Patterns:
- Design 1 (Double Rotated Square / 8-pointed star):
REPEAT 2 [REPEAT 4 [FD 80 RT 90] RT 45] - Design 2 (Rotated Pentagon Rosette – 8 pentagons):
REPEAT 8 [REPEAT 5 [FD 60 RT 72] RT 45] - Design 3 (Rotated Star/Diamond Pattern):
REPEAT 12 [REPEAT 4 [FD 60 RT 90] RT 30] - Design 4 (Flower with 8 Circular Petals):
REPEAT 8 [REPEAT 180 [FD 1 RT 2] RT 45]
3. Write the full forms of the following commands:
| Short Form | Full Form (Command Name) | Function & Purpose |
|---|---|---|
| PD | Pen Down | Instructs the turtle to put its drawing pen down so that it leaves a trace when moving. |
| HT | Hide Turtle | Hides the turtle triangle from the screen so the user can view the complete drawing unobstructed. |
| PU | Pen Up | Lifts the turtle’s pen up so it can move anywhere on the screen without drawing any line. |
| ST | Show Turtle | Makes the hidden turtle reappear on the screen. |
| PE | Pen Erase | Sets the turtle pen into eraser mode; when moved over existing lines, it erases them. |
Frequently Asked Questions (FAQ)
Q1: What is the main benefit of using the REPEAT command?
Ans: The REPEAT command reduces coding effort and time by running multiple commands in a single line instead of typing the same instructions again and again.
Q2: Why do we use PU (Pen Up) and PD (Pen Down)?
Ans: PU allows the turtle to jump to a new position without leaving an unwanted line. Once the turtle is at the desired location, PD is used to resume drawing.