shinyhappypeople Posted February 11, 2013 Share Posted February 11, 2013 Why is the formula for finding the formula area of an equilateral triangle so different from finding the area of other triangles? Quote Link to comment Share on other sites More sharing options...

Dana Posted February 11, 2013 Share Posted February 11, 2013 Area of any triangle is 1/2 base x height. Equilateral is no different. Quote Link to comment Share on other sites More sharing options...

Dana Posted February 11, 2013 Share Posted February 11, 2013 I suppose you could find the height and write the formula for area in terms of the base (one side), but I don't know why you'd bother learning it separately. Quote Link to comment Share on other sites More sharing options...

Lolly Posted February 11, 2013 Share Posted February 11, 2013 Why is the formula for finding the formula area of an equilateral triangle so different from finding the area of other triangles? Curious as to what math book you are using? I've never seen a special formula for the area of an equilateral triangle. Same one works on them as on any other. Quote Link to comment Share on other sites More sharing options...

shinyhappypeople Posted February 11, 2013 Author Share Posted February 11, 2013 Curious as to what math book you are using? I've never seen a special formula for the area of an equilateral triangle. Same one works on them as on any other. I'm not using a math book. I'm working my way through Khan academy and using the 1/2bh formula doesn't give the correct answer. Khan Academy using uses this formula: Equilateral Triangle s = length of a side If you have a triangle that has sides of 10 in, using 1/2 bh the area is 50 sq in. (did I do that right?) Using the other formula, the area is 43.301 sq in. (equilateral triangle area calculator) I don't understand why that is, and it's driving me nuts!! Quote Link to comment Share on other sites More sharing options...

Arcadia Posted February 11, 2013 Share Posted February 11, 2013 The height is the perpendicular height. So 1/2 bh = 1/2 (10)(square root of 75) = 43.3 You can get the height by Pythagoras theorem. Squared of base + squared of perpendicular height = squared of slant height Squared of 5 + squared of h = squared of 10 25 + squared of h = 109 Squared of h = 75 h = square root of 75 ETA: http://mathcentral.uregina.ca/QQ/database/QQ.09.03/jared1.html The page has a pictorial explanation for how to get area of an equilateral triangle. Quote Link to comment Share on other sites More sharing options...

shinyhappypeople Posted February 11, 2013 Author Share Posted February 11, 2013 The height is the perpendicular height. So 1/2 bh = 1/2 (10)(square root of 75) = 43.3 You can get the height by Pythagoras theorem. Squared of base + squared of perpendicular height = squared of slant height Squared of 5 + squared of h = squared of 10 25 + squared of h = 109 Squared of h = 75 h = square root of 75 ETA: http://mathcentral.u....03/jared1.html The page has a pictorial explanation for how to get area of an equilateral triangle. Thanks! I can sleep now :) Quote Link to comment Share on other sites More sharing options...

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