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## Geometry 222-226

### Unit 1: Lesson 5

Constructing triangles

# Construct a right isosceles triangle

Can you build a triangle that is both a right triangle and an isosceles triangle? Created by Sal Khan.

## Want to join the conversation?

• If you had a quadrilateral for which you knew all 4 sides, have you uniquely determined it? Are there other quadrilaterals with the same 4 sides but different angles?
• Nice question and the answer is that there can be other quadrilaterals with same side lengths but different angles. For example, both squares and rhombi have equal side lengths for all 4 sides, but a square is restricted to only have right angles while a rhombus is not.
• unique triangle.. what about reflected triangles? they would have the same lengths!
• That would be the same triangle. The question is asking, can you make another triangle that has at least one different angle or side length.
• Can someone explain me one a few things here because I didn't really understand much. like what if you need to make a 80 degree triangle with a 9 inch side? how am I supposed to find out if it even can be made or if its not a unique triangle? I'm bad at making triangles for math so I need some help to figure out how to know. I feel like this is a stupid question. (T-T)
• If it is a right isosceles triangle, you would first make the 90 degree angle. Then you would drag the other two points until the side across from the 90 degree angle is 9 inches and the other two sides are equal.
If you are making an isosceles triangle with just a 80 degree corner and no 90, then you would first make the 9 inch side, then drag the corner across from it until it is 80 degrees, then make the last two sides of the triangle equal.
Hope this helps!
• I am having a lot of trouble on this topic... could you please add maybe another problem in this video?
• you can use a pro tracker to measure the angles,,,thats what i use
• i still cant perfect the triangle i keep messing up any advice ?
• Triangles can be very challenging, but like everything else if you have a good understanding of the basics you can often work them out.
Try going back to the shape questions for year k through to year 8. Many primary teachers skip over teaching shapes quickly by focusing on vertices, faces, edges, labeling common shapes, 2d and 3d shapes' perimeter, area and volume and when it comes to angles as long as you can use a protractor you can work out the rest.
The integration and extension of shapes and angles together is missed due to lack of teacher interest or more frequently lack of time.
Finding and filling gaps in a person's knowledge then falls to the individual to take responsibility for and with math on Kahn academy you have all you need to go right back to the start.
Enjoy the journey.