# Drawing Triangles (Part 1)

Warmup

The triangle shown above are similar triangles. can you explain why?

Activity #1

To Construct an Equilateral Triangle. Follow the instructions below to construct an Equilateral Triangle. If you get confused, pause and watch the video below.

• Click the Regular Polygon icon. • Click on the screen in two places and a dialog box pops up.
• Type 3 and press Enter on your key board.
• An equilateral triangle will be created.
• Click on the Distance or Length tool. • Click each side of the triangle and the lengths of the sides will be labeled.
• Click on the Angle tool. • Click on the triangle and all the angles will be marked.
• Play around with the vertices of the triangle to confirm that the side lengths and angles remain the same.

Activity #2

To Construct an Isosceles Triangle. • Follow the instructions below to construct an isosceles Triangle. If you get confused, pause and watch the video below.

Activity #3

How to construct a triangle given two angle measures and one side length. • Use Angle 1 and Angle 2 sliders to choose two acute angles.​
• Use slide AB to choose a side length. Side length CA is not constrained. ​
• So grab point C and slide it up or down to create a triangle. B is just a point, so go slowly as you approach it. When the line snaps on B, a triangle will be created as you’ll see all three sides and angles.

Challenge #1

(1.) Use the protractor in the applet below to draw a triangle where one angle measures 20° and another angle measures 45°.

(2.) Use the protractor in the applet below to draw a triangle where one angle measures 120° and another angle measures 50°.

Challenge #2

Use the protractor in the applet below to draw a triangle where one angle measures 90° and another angle measures 100°.

Which of the above three triangles is impossible to draw?

Challenge #3

In the diagram below, 9 toothpicks are used to make three equilateral triangles. Figure out a way to move only 3 of the toothpicks so that the diagram has exactly 5 equilateral triangles.

Quiz Time