grade lớp 10 level phổ thông difficulty easy updated 06/10/2026

Drawing the national flag with Inkscape

Tóm lược nội dung

This lesson provides step-by-step instructions for basic operations in Inkscape to create the national flag, including:

• Creating and saving vector graphics files
• Drawing and setting dimensions for rectangles and stars
• Setting fill and stroke colors
• Aligning objects using the Align and Distribute tool

Creating and saving files

1. Create a new file

   Select File > New from the main menu.

2. Save the file

   Select File > Save As... from the main menu.

   In the save dialog box:

   • Navigate to the drive and folder where you want to save the file.
   • File name: enter vietnam-flag.
   • Save as type: leave the default extension Inkscape SVG (*.svg).
   • Click Save.

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Drawing the flag

1. Select the rectangle tool

   On the left toolbar, select the Rectangle tool (shortcut R).

   

2. Remove the stroke

   In the color palette at the bottom, right-click the transparent color box (marked with an X) > select Set stroke.

   

3. Set the red fill color

   In the color palette, right-click the red color box > select Set fill.

   

4. Draw the rectangle

   Click and drag the mouse to draw a rectangle of any size.

5. Set the dimensions

   • Enter the width W: 300.
   • Enter the height H: 200.

   

   Note:
   After resizing, the rectangle may extend beyond the page boundary. This is completely normal in vector graphics and does not affect the actual drawing elements.

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Drawing the star

1. Deselect the rectangle

   Simply click anywhere on an empty area.

2. Select the star tool

   On the left toolbar, select the Star/Polygon Tool

   

3. Draw the star

   Click and drag the mouse to draw a star of any size.

   Note:
   The star may appear tilted at this stage; it will be adjusted in a later step.

4. Shape the star

   To proportion the star points correctly, enter a Spoke ratio value: 0.38 (1).

   1. Let \(r\) and \(R\) represent the inner radius and outer radius of the star, respectively.

      The standard ratio between these two radii according to the "golden ratio" formula is: \(\frac{r}{R} = \frac{1}{\varphi^2}\)

      Where: \(\varphi = \frac{1 + \sqrt{5}}{2} \approx 1.618\)

      Therefore: \(\frac{r}{R} = \frac{1}{1.618^2} \approx 0.381982\)

      Thus, \(r\) can be rounded to \(r \approx 0.38 R\).

   

5. Rotate the star

   Click the star a second time (1), then drag a corner handle to rotate it upright.

   1. In Inkscape, there are two object selection modes:

      • First click: displays straight handles used for resizing.
      • Second click: displays curved handles used for rotating.

   

6. Set the dimensions

   Enter the dimensions for the star:

   • Enter width W: 114

   • Enter height H: 108.5 (1)

     1. Basis for calculating the star's dimensions:

        The flag has a length of \(3a = 300\) and a width of \(2a = 200\).

        The radius of the circumscribed circle of the star is \(R = \frac{3a}{5} = 60\).

        Based on trigonometric formulas, we have:

        • Width: \(W = 2R \cdot \sin(72^\circ) \approx 114\)
        • Height: \(H = R \cdot (1 + \cos(36^\circ)) \approx 108.5\)

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Centering the star on the flag

1. Select both objects

   • Click to select the flag.
   • Press and hold the Shift key and click to select the star.

2. Center the star on the flag

   • Select Object from the main menu > select Align and Distribute...
   • In the panel on the right, under Relative to: select First selected, which aligns objects relative to the first selected object (in this case, the flag).
   • Click the following two alignment buttons in sequence: center on vertical axis and center on horizontal axis.

   

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Grouping and locking the aspect ratio of objects

1. Group the objects

   With both the flag and star selected, right-click > select Group [or press ++ctrl+g++] to combine both into a single object.

   

2. Lock the aspect ratio

   On the Tool Controls bar, click the lock icon button to lock the proportion between width and height.

   

3. Resize the drawing

   In the width field W, enter 150 to scale down the flag.

   The height H will automatically adjust proportionally to 100 without distortion.

4. Save the file

   Press Ctrl+S to save the file. Completed.

   Note:
   It is recommended to save your work frequently during the drawing process.

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Sample drawing

The completed drawing file is available on GitHub.

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Some English words

Vietnamese	Tiếng Anh
căn chỉnh (các đối tượng)	align (objects)
chiều cao	height
chiều rộng	width
chọn màu đường viền	set strike
chọn màu nền	set fill
gom nhóm	group