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The law of cotangents
Deriving the law of cotangents using the inradius of a triangle. #math #maths #mathematics #geometry #trigonometry
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3 likes

cosA × cos B - sin A × sin B = cos(A+B)
This is an obscure derivation of a well-known trigonometric identity. #math #maths #mathematics #geometry #trigonometry
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4 likes

The triple cotangent identity
Several formulae are derived from locating the incenter of a triangle. The incenter is formed by the angle bisectors meeting concurrently. #math #maths #mathematics #geometry #trigonometry
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6 likes

The incircle, inradius and equating area formulae
The area of a triangle can be found using the inradius. Using Heron’s formula, one can find the length of the circumradius and the inradius using just the side lengths of the triangle. #math #maths #mathematics #geometry #trigonometry
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Deriving Heron’s formula using the circumradius of the triangle
Heron’s formula is a useful formula to find the area of a triangle using only the triangle’s side lengths. This is a lesser-known derivation of the formula, but quite a cool one nonetheless. #math #maths #mathemati cs #geometry #trigonometry
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Find lengths in terms of the sides
O is the orthocenter of the triangle ABC. The lengths centered around point O and the lengths of the orthic triangle DEF are solved in terms of the side lengths. The area of the triangle is found with Heron’s formula. #math #maths #mathemati cs #geometry #trigonometry
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Side length in the orthic triangle
The orthic triangle is the triangle made by connecting the points where each altitude meets their corresponding side. Since orthocenter is the common meeting point of the quadrilaterals, then three cyclic quadrilaterals are formed, so Ptolemy’s theorem can be used to find the lengths of the sides o
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Simplifying the distance between two points in the heptagonal triangle
In a prior post, I derived the distance formula between the orthocenter and the circumcenter using a complicated argument involving similar triangles. In this post, I used a simple formula to get the required answer. #math #maths #maths #geometry #trigonometry
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The distance between the orthocenter and the circumcenter of a triangle
In any acute triangle, the distance between the orthocenter and the circumcenter is found with quite a nice formula that relate the sides and the circumradius. #math #maths #mathematics #geometry #trigonometry
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Connecting the orthocenter to the vertices
In any acute triangle ABC, the distances from the orthocenter (where the altitudes meet) to the vertices are of the form 2R × cos Ε, where E is one of the angles of the triangle. R is the length of the circumradius of the triangle. #math #maths #mathematics #geometry #trigonometry
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Any number of the form 4n+3 cannot be expressed as the sum of two squares.
This is a fact that comes from elementary number theory. If you have a number that has a remainder of 3 when divided by 4, it can’t be written as a sum of two square numbers. Numbers like 7, 11, 15 etc. can’t be written in that form.
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Deriving the formula to find Pythagorean triples
Given natural number m, n such that m > n > 0, then the derived formulae can be used to find Pythagorean triples. Pythagorean triples are sets of three whole numbers that satisfy the Pythagorean theorem. #math #maths #mathematics #geometry #trigonometry
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46 likes

Proofs of some prime number properties
These are two proofs for why prime numbers revolve around multiples of 4 and multiples of 6. #math #maths #mathematics #algebra #arithmetic
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3 likes

(1² + 1²) × (1² + 2²) = 1² + 3²
This is one of my favorite numeric truths and it has a pleasant geometric interpretation to go with it. Take three squares and construct the diagonals as shown in the diagram. The product of the length of the two shorter diagrams is equal to the length of the longest diagonal. #math #maths
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Rules for parity arithmetic and their proofs
Assuming the unknowns are integers, then the following rules for parity addition and parity multiplication holds true. Parity is the state of an integer when it’s divided by 2. All integers take the form of either 2x (even) or 2x+1 (odd) where x is any integer. #math #maths #mathematics
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Two squares times two squares makes two squares
The sum of two squares times the sum of another two squares equals the sum of yet another two squares. These formulae are used to find examples like 5 × 13 = (2²+1²) × (2²+3²) = 65 = 8²+1² = 7²+4². #math #maths #mathematics #algebra #arithmetic
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If p is prime & p>3, then p²-1 is divisible by 24.
Two proofs of a result that’s based around prime numbers. For example, 11² - 1 = 120 = 24×5. #math #maths #mathemati cs #algebra #arithmetic
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3 likes

Proof of the Pythagorean Theorem, part 3
Here’s another classic proof of the Pythagorean Theorem where four triangles are placed in such a way that a small square in the middle of them. From there, an equating of areas occurs. #math #maths #mathematics #geometry #trigonometry
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6 likes

Proof of the Pythagorean Theorem, part 2
This is an augmented version of the first proof discovered by US President James Garfield. By slicing the original diagram in half, a trapezoid is created with three right triangles overlaying it so an equating of areas can occur. #math #maths #mathematics #geometry #trigonometry
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5 likes

Proof of the Pythagorean Theorem, part 1
This is one of my favorite geometric proofs. It’s basically a square that’s twisted into a larger square so an equating of areas occurs. #math #maths #mathematics #geometry #trigonometry
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heptagon14

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I post math stuff here