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.

6703 questions
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In a triangle $ABC$, $AB = a-b$ and $BC = 2\sqrt{ab}$, then find $\angle B$?

Is this question solvable? In $\Delta ABC$, $AB = a-b$ and $BC = 2\sqrt{ab}$, then $\angle B$ is (a) $\: 60^{\circ}$ (b) $\: 30^{\circ}$ (c) $\: 90^{\circ}$ (d) $\: 45^{\circ}$
Kun
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Heron's formula, mensuration, areas

A right triangle has perimeter 144 cm and hypotenuse 65 cm find its base and height. Also find its area using heron's formula This is the question. If any one knows how to solve then please help
ACDC
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A box contains 5 rods whose lengths make triangles.

A box contains five rods whose lengths are 1", 3", 6", 10", 15". How many different obtuse triangles can be made using only three rods at a time. I determined that the answer is 1 because the triangle inequality nullified the others without using…
Ian L
  • 889
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Finding angles in a triangle

If $AD$ is the median to side $BC$ of $\Delta ABC$ & $\angle B =2 \angle C$, then find $\angle B$ I feel something is missing in the question
Amritanshu
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Catalog of triangles

Is there a catalogue of triangles in which one might find for instance the name of the right angle triangle with an angle of approx 35 degrees in which the altitude, median and side bisectors intersect at a point? Or in which the diameters of the…
prb
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How to calculate coordinates of third point in a triangle (2D) knowing 2 points coordinates, all lenghts and all angles

I have a triangle and I know the coordinates of two vertices: $A=(x_1,y_1), B=(x_2,y_2)$ All the angles: $ABC = 90^\circ, CAB = 30^\circ$ and $BCA = 60^\circ$ and all the edge lengths. How can I find the coordonates of the third verix…
Daniel Dudas
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Length of the side of a discrete equilateral triangle from area

Firstly I haven't practised any mathematics in a long time, I understand that this might be pretty basic for math.stackexhcange, but I cannot seem to find any answers on the internet anywhere! I've come across this problem at work, where basically…
Max Chandler
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triangles in a grid of $n\times n$ with positive coordinates

I need to count the number of triangles formed in a grid of $n\times n$ with positive integer coordinates $(0..n)$. For example for $n = 1$ the answer is 4.
viktor
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How to proof that those triangles are similar?

I have given that : The triangle ABC Isosceles triangle(AC = BC) The angle at the base is 72 degrees There is a bisector L for the angle A I have to proof that the triangle ABC is similar to the triangle BLA So far I have found that: The angles…
Planet_Earth
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Right triangle and Sine function?

Given two angles and the hypotenuse of a right triangle, when trying to find the length of the side opposite the given angle, why and how does it's angle and supplementary angle yield the same answer? For example. Right triangle hypotenuse = 5 angle…
math noob
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Find all triangles with a fixed base and opposite angle

I have a situation where I know the cartesian coordinates of the 2 vertices of a triangle that form its base, hence I know the length of the base and this is fixed. I also know the angle opposite the base and this is also fixed. Now what I want to…
bph
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Find the Vertices of a Triangle from Set of Points

I have a set of cartesian x,y points which I know am fairly certain are on the edges of a triangle. What is the easiest way (either algebraically or algorithmically) to identify what the three vertices of the triangle are? The set of points may or…
Richard
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Counting right triangles with integral hypotenuse and given integral height

Let h = the height of the right triangle (an integer). Let c = the hypotenuse Let l = the other leg So l^2+h^2=c^2 I am trying to figure out, for instance, why there are 8 such triangles when h=12. I try to figure this out manually and I'm only…
AOAOne
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What do you call the point where two lines meet?

This is from a third grader. His example is the point where the hands on the clock meet. It's not pivot. Or "if you start with a dot and make two lines go out from it, on straight up and one to the left, what would the dot you started at be…
jqning
  • 129
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Determine length from sketch

I have a simple problem that I need to solve. Given a height (in blue), and an angle (eg: 60-degrees), I need to determine the length of the line in red, based on where the green line ends. The green line comes from the top of the blue line and is…
Adam
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