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# Worked example: Classifying triangles

## Thuyết minh video

categorize the following triangles according to whether they're 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 then 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 kind of visual judgment so I would say that this is obtuse and Bango 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 to not up twos to obtuse check our answer let's do a couple more of these which of the following are correct descriptions of triangle P IG or I guess triangle pig select all that apply P IG is equilateral well that's not true to be equilateral all the sides have to be the same length and you see here two sides or seven but one side has length 4 so that's not true angle P IG has two equal angles well we see that right over here 74 these two angles that are 74 degrees so that's true angle triangle P triangle pig I kiss 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 Pio ji has three acute angles well that is true all of these angles are less than 90 degrees triangle P IG has a right angle no none of these angles are exactly 90 degrees so it isn't or it is not does not have a right angle so let's check our answer let's do one more of 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 like that it's really a scalene triangle here we have two sides that are the same lengths but the third is different this would be an Solly's triangle but it's not equilateral and here they're all the same length so we have an equilateral triangle we got it right