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Construct a right isosceles triangle

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

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  • leaf red style avatar for user Victor Azmanov
    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?
    (2 votes)
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    • mr pink red style avatar for user andrewp18
      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.
      (3 votes)
  • male robot johnny style avatar for user petkoaus000
    I can't hear the person talk please help!
    (3 votes)
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  • duskpin tree style avatar for user Rodriguez, Keilani
    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)
    (2 votes)
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    • piceratops ultimate style avatar for user Jacob Miller
      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!
      (2 votes)
  • duskpin ultimate style avatar for user Shruti Marota
    I am having a lot of trouble on this topic... could you please add maybe another problem in this video?
    (2 votes)
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  • leafers ultimate style avatar for user Peter Wraae Marino
    unique triangle.. what about reflected triangles? they would have the same lengths!
    (2 votes)
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  • starky sapling style avatar for user kurt kobain
    i still cant perfect the triangle i keep messing up any advice ?
    (2 votes)
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    • primosaur ultimate style avatar for user Duncan Gillespie
      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.
      (2 votes)
  • piceratops ultimate style avatar for user peytonstahl
    do i use a protractor for some questions on constucting triangles if not can you give me a step by step instuction to solve a problem
    -thank you
    (2 votes)
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  • piceratops ultimate style avatar for user Nguyen, Justin
    Wait didn't you just make one at ?
    (2 votes)
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  • blobby green style avatar for user Saman Syed
    A Shape has 3 equal sides that are each 4 cm in length right angle. How can draw best shape?
    (2 votes)
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  • aqualine ultimate style avatar for user Blake hoffman
    How do i make a right triangle wth sides 5,8,and 10
    (2 votes)
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Video transcript

They're asking us to draw a right triangle. So that means it has to have a 90-degree angle. But it's also an isosceles triangle, so that means it has to have at least two sides equal and has two sides of length 3. So those two sides that are going to be equal are going to be of length 3, and it's got to be a right triangle. So let's see if we can do that. So let's try to make this right over here the right angle. And let's make this side and this side have length 3, so 3 and then 3 right over there. Let me make sure I get that right angle right. OK, there you go. So it's a right angle. It's isosceles. At least two sides are equal. And the two sides have length 3. So it seems like we've met all of our constraints. Now they say, is there a unique triangle that satisfies this condition? So another way of rephrasing that, is this the only triangle that I could have drawn that meets these conditions? Well. I can't change this angle if I want to meet these conditions. I can't change these two lengths. And if you keep this angle constant and you keep these two lengths constant, then this point and this point are going to be there are no matter what. So this is the only side that can connect those two points. So this is the only triangle that meets those conditions. You can't have different side lengths, or you couldn't have different angles right over here and also meet those conditions. So is there a unique triangle that satisfies the given conditions? Yes, there's only one unique triangle.