Worked example: Classifying triangles
Work through sample problems categorizing triangles as scalene, isosceles, equilateral, acute, right, or obtuse. Created by Sal Khan.
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- If I have two angles that make no sense like 30, 130 and the third
one is missing how do I find the answer?(7 votes)
- All the angles of a triangle add up to 180 degrees, so if you have two of the measures, you add up the two measures given and then subtract it from 180 to get the third measure. If you want to test if a triangle adds up to 180 degrees, you can cut out a triangle out of paper and then tear of the three corners. Then, on another piece of paper, you draw a straight line because a straight line is 180 degrees. You put all the corners of your triangle on the line and it should fit.(23 votes)
- vote this up please and thank you
Goal: <250(13 votes)
- I'm going to 4th grade this year and I want to improve my reading. And also, I'm looking forward to getting mostly 4’s and 3's on my report card (We grade by 1,2,3,4 with 1 being the worst and 4 being the best.) Any Tips? Thank you very much.(6 votes)
- Practice, practice, practice. Make a study schedule and stick to it. Go over notes you get in class and if you have a hard time understanding something you read or something in class, read it again or ask the teacher to explain it. Ask relevant questions, that always helps. DO NOT fall asleep in class.
To improve in reading, try reading books that challenge you but don't overwhelm you. Experiment a bit to find what books would interest you specifically. If your up to it, try going for books with different styles. By style I mean how its spoken and written. Examples are British vs. American (slight differences in dialect). Or Shakespearean vs. slang (HUGE DIFFERENCE). This helps broaden vocabulary and will definitely help you understand plot and setting better.
Hope this helped. Good luck in fourth grade!!(11 votes)
- Can a equilateral triangle be a scalene triangle?(4 votes)
- A scalene triangle means all sides have a different length. An equilateral triangle means all sides are the same length.(10 votes)
- Obtuse what is it i don't know?(5 votes)
- obtuse angles are angles which measures above 90 degrees and below 180 degrees(7 votes)
- Why do we have to classify shapes?(4 votes)
- It makes them a lot easier to talk about if they have names and labels that we can agree on.(6 votes)
- i need help on something ules than tis(3 votes)
- "Boi" is not a word in the English dictionary(6 votes)
- at0:39I didn't hear what he was saying(4 votes)
- If you ever have trouble understanding what Sal is saying, you can use the transcripts below the videos.
Around0:39he said: "...we can assume that these are drawn to scale, so we can base it on our visual judgement. So I would say that this is obtuse..."(4 votes)
- in the part were u made us guess the triangles you should have switched the order so we could actully guess but this is well it helped thank u(5 votes)
- how do you determine if it is a right triangle or a acute triangle.(5 votes)
- Right Angle: Exactly 90°, less than an obtuse angle and bigger than an acute angle.
Acute Angle: Below/Less than 90°, smaller than a right angle and an obtuse angle.(1 vote)
Categorize the following triangles according to whether or not they are obtuse triangles. So an obtuse triangle is a triangle that has an obtuse angle in it, or an angle that is larger than 90 degrees. So it's pretty clear that this one does not have any obtuse angles. This is a 90 degree angle, and these are going to have to be less than 90 degrees. So this is not obtuse. This one right over here, just by looking at it, you see that all of them are less than 90 degrees, so I'll put this not obtuse. Now, these two are interesting. Angle JKL looks like it is larger than 90 degrees, and we can assume that these are drawn to scale, so we can base it on our visual judgment. So I would say that this is obtuse, and angle BAC also looks like it is larger than 90 degrees. So that's an obtuse angle, so I would throw that in the obtuse bucket as well. So we had two not obtuse, two obtuse. Check our answer. Let's do a couple more of these. Which of the following are correct descriptions of triangle PIG? Or I guess triangle pig? Select all that apply. PIG is equilateral. Well, that's not true. To be equilateral, all the sides have to be the same length. And we see here two sides are seven, but one side has length 4. So that's not true. Angle PIG has two equal angles. Well, we see that right over here, these two angles that are 74 degrees. So that's true. Triangle PIG, I guess, has an obtuse angle. Well, an obtuse angle is one that's larger than 90 degrees. None of these are larger than 90. That's not true. Triangle PIG has three acute angles. Well, that is true. All of these angles are less than 90 degrees. Triangle PIG has a right angle. No, none of these angles are exactly 90 degrees, so it does not have a right angle. So let's check our answer. Let's do one more of this. This is actually kind of fun. Categorize the following triangles according to whether or not they are equilateral. So to be equilateral, all of the sides have to have the same length. So this is equilateral. This one, the sides are definitely not the same length. In fact, not even two of the sides are the same length. That's really a scalene triangle. Here we have two sides that are the same length, but the third is different. This would be an isosceles triangle, but it's not equilateral. And here they're all the same length, so we have an equilateral triangle. We got it right.