Mathematics Stack Exchange
Mathematics Stack Exchange

Questions tagged [triangles]

For questions about properties and applications of triangles.

A triangle is a polygon with three sides. It is an important geometric figure, because any polygon can be subdivided into triangles.

Triangles can be classified by the number of sides they have that have equal length

  • All three sides of an equilateral triangle have equal length.
  • An isosceles triangle has at least two sides of equal length.
  • A scalene triangle is a triangle that is not isosceles, that is, it has no sides with equal length.

A triangle may also be classified by describing its angles. A triangle is said to be a right triangle if it contains a right angle, and obtuse triangle if it contains an obtuse angle, or an acute triangle if all three of its angles are acute.

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Calculating radius of the circle

A perfect circle sits exactly within a right-angled triangle,dividing its hypotenuse into two segments of 3 and 10 units. The area of the triangle is 30 square units. What's the radius of the circle, "r" ?
Rishi
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Is there a reflex angle symbol?

I only knew this angle symbol "$\angle$", which is usually used to represent acute angles. But now I have accounted a problem, where I wanted to represent the reflex symbol of $\angle ABC$. I know, I can simply say "The reflex $\angle$ of $\angle…
Daniel Cheung
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Prove that triangle is equilateral

I have a triangle here, how do I prove that $BCD$ is equilateral(so all lines have the same length) And yes this is 2D What I have so far is $$BAC = 120^\circ$$ So how do I point out that $$BCD = 60^\circ$$ $$CBD = 60^\circ$$ $$BDC =…
Mazzy
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$m$ be the number of distinct non congruent integer sided triangles each with perimeter $15$

Let $m$ be the number of distinct non congruent integer sided triangles each with perimeter $15$ and $n$ be the number of distinct non congruent integer sided triangles each with perimeter $16$ Then $m-n=?$ a) -2 b) 0 c) 2 d) -4 did not get the…
Myshkin
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Formula for the length of line that connects two sides of a triangle.

For the triangle in the picture, coordinates of $A$, $B$ and $C$ are known. Is there an explicit formula for length $XY$, as a function of height $h$? It's a function of other variables as well, but it's important that it depends explicitly on…
enedene
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Simple Triangle Completion

How do you find the missing point of a triangle, given: 2/3 of the points, two slopes, and one angle of direction. Here's the problem. There are two points: Point B (1,1), showing an arrow going up (an undefined slope). Point A (3,4), with a 45…
Arc
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non right angle triangle - solve for B when b, A and a are known

I'm trying to work out the two possible values for B when A, a and b are all known. I'm certain its possible but I'm not sure how to start or what theories to look for to solve the question as my math is severely lacking. Any pointers on how to…
jonathan topf
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Determine the exact location of the centroid?

This is my last question for the day! :P Usually I am good at math but I've been sick for over a year and am now finding it hard to concentrate. :P Triangle CDE has vertices C(-2,4), D(6,2), and E(-4, -2). Determine the exact location of the…
Madymino
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How would you measure a right triangle with sides of 1 and root 2?

This may be a silly question, but I saw this diagram on wikipedia and was intrigued: https://en.wikipedia.org/wiki/File:Square_root_of_2_triangle.svg How would such a triangle work in real life? It's in theory possible to draw two side lengths of…
Graeme
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Fastest way to check whether the triangle inequality is satisfied

If we are given the lengths of the three sides of a triangle, and we simply add the 2 smallest sides and check to see if the sum is larger than the third side, will this always yield the correct answer i.e. will it always tell us if the triangle is…
Joebevo
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If two collinear vertices of a degenerate triangle are equal, Why two of the angles in such triangle are undefined, and which angles exactly?

I am trying to understand the angle and side measurements of triangles that are degenerate. There are 3 types of these triangles: https://en.wikipedia.org/wiki/Degeneracy_(mathematics)#Triangle For the one whose 2 vertices are equal, they state…
bp2017
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How can I work out the formula for Wind Downwarde6b

I want to write a step by step guide on how to do Wind up and Wind down calculations using the CRP / E6B. I have a prototype Excel but need to work out the 25 drift @ 114 and how to loop until the drifts match [G22] Wind up is working using B26 is…
Michael Blake
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Sides from angles of a triangle

How does one find the side lengths of a right triangle in relation to each other using just the angles? I have all three angles. Is this even possible?
user1814893
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Angle in triangle

Angle BAC = $70^o$ , Angle ABE = Angle EBC. Find angle BOC Let angle ABE = $\alpha$ and angle BOC = $\beta$ Angle ACB = $110^o - 2\alpha$ Angle AEB = $110^o-\alpha $ Angle FOE = $\beta$ Angle AFO = $180^0-\beta +\alpha$ Angle BFC = $\beta -…
Magenta
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How to determine the edge points of a line segment passing through a point on a ternary diagram

I'm working with ternary diagrams as a (hopefully convenient) way to lay out patterns in a triangle. Briefly, (From Wikipedia:) "A ternary plot, ternary graph, triangle plot, simplex plot, Gibbs triangle or de Finetti diagram is a barycentric plot…
Bald Eagle
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