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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Solve the right triangle? Round decimals to the nearest tenth?

Image of the triangle There is a right triangle DEF with the adjacent is 12 and the acute angle of D being 25 degrees and E being the right angle... I have to figure out angle F, DF, and DE... I'm honestly not sure on what to do and i'm stressing…
danneh
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congruent triangle question

There are two triangles ABC and DEF with corresponding sides abc and def. Given that angle D = angle E, and angle A = angle C, and side b = side e, determine if the triangles are congruent. The answer is yes based on the theorem that two angles and…
user122415
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Proving orthocentre of outer triangle is incentre of the triangle formed by the feet of perpendiculars

This questions is related to the question before. I was mistaken. Because I thought ED and AB are parallel, but they're not. So this question made me really confused and curious about it. Given a Triangle ABC. AD, BE, and CF are altitudes. Prove…
Annita
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How can I prove that DEF is an equilateral triangle?

TRIANGLE ABC IS EQUILATERAL AND I drawed the picture fast but, AD=BE=CF (Large Version) With this information I should be able to prove that DEF is an equilateral triangle. Could anyone help me out?
Hi there
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Find the point that makes two triangle equal

Can anyone help me with this problem? I draw the graph according to the problem, but don't know how to solve the problem. Thanks. A triangle has vertices with coordinates A(0,15), B(0,0), and C(10,0). Find the coordinates of point D on AC so that…
learning
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Solutions of triangles problem

Prove that $$\left(a-b\right)^2\cos^2 \left(\frac{C}{2}\right) + \left(a+b\right)^2\sin^2\left(\frac{C}{2}\right)=c^2$$ My solution:- I don't know what to do next..please give some hint. Or point out if I am wrong somewhere..
danny
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Determine the area of triangle PQR in terms of triangle XYZ

Any Ideas on How to Begin ? Begin Many Thanks
user360471
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Find the shortest side if

In the $\triangle PQR$ angle P= 60 degrees & angle Q= 90 degrees . Find the length of the shortest side. Any Ideas on how to begin Many Thanks :)
user360471
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Finding lengths of a triangle with only one angle and its length.

I have a paint program that does not deal with angles. Drawing a straight line will only get point of origin and length, no matter where you draw it to. So, I need to draw a line 570 mm or pixels, at a 35 degree angle. Thus I need the vertical…
S R Hampton
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Finding length and width of old square

The area of new shape is $A=130$ m$^2$. The original square had $2$ m added to its width and $5$ m to its length, the problems asks for one of the original sides (since they're all equal of course). How can I go about this? I figured $130$…
Johnnygood
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"Easy" triangle problem (hight school)

Can someone give me a hint to this "easy" problem? In the triangle ABC, we have: DE || BC, FE||DC, AF=1, FD=2, find DB=?
Maxtron Moon
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Finding the third side of a triangle given the area

I know the area and the lengths of two sides (a and b) of a non-right triangle. I also know P1 (vertex between a and c) and P2 (vertex between a and b). I already know this much: Perimeter = $ \frac{(a+b+c)}{2} $ Area = $ A=\sqrt{p(p-a)(p-b)(p-c)}…
Seth
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How do I find the height of a triangle when it is tilted downwards at one end?

In the first pic, it is shown that the height of the triangle is $1.5$ m. In the second pic, the point $C$ is moved to point B. How do I find height $h$ so that the perpendicular height of the triangle stays the same at $1.5$ m?
John Evans Solachuk
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Finding the circumcentre

Suppose angle ACB is 90°, why is p the circumcentre of triangle ACB? I can only proove that RP is the perpendicular bisector but what is it to do with angle ACB?
Estudiantekriss
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How to calculate the X distance while Z object is moving top to bottom?

First of all, sorry for my extremely low knowledge about mathematics. All i am able to do is this image which describe the problem. Image of triangle + information I want to know that how can i calculate the X distance each time while Z object is…
Shahrukh Khan
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