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  2. List of trigonometric identities - Wikipedia

    en.wikipedia.org/wiki/List_of_trigonometric...

    Ptolemy's theorem states that the sum of the products of the lengths of opposite sides is equal to the product of the lengths of the diagonals. When those side-lengths are expressed in terms of the sin and cos values shown in the figure above, this yields the angle sum trigonometric identity for sine: sin(α + β) = sin α cos β + cos α sin β.

  3. Proofs of trigonometric identities - Wikipedia

    en.wikipedia.org/wiki/Proofs_of_trigonometric...

    Two angles whose sum is π/2 radians (90 degrees) are complementary. In the diagram, the angles at vertices A and B are complementary, so we can exchange a and b, and change θ to π/2 − θ, obtaining: ⁡ (/) = ⁡

  4. Sum of angles of a triangle - Wikipedia

    en.wikipedia.org/wiki/Sum_of_angles_of_a_triangle

    Triangle area property: The area of a triangle can be as large as we please. Three points property: Three points either lie on a line or lie on a circle. Pythagoras' theorem: In a right-angled triangle, the square of the hypotenuse equals the sum of the squares of the other two sides. [1]

  5. Euclidean geometry - Wikipedia

    en.wikipedia.org/wiki/Euclidean_geometry

    The triangle angle sum theorem states that the sum of the three angles of any triangle, in this case angles α, β, and γ, will always equal 180 degrees. The Pythagorean theorem states that the sum of the areas of the two squares on the legs ( a and b ) of a right triangle equals the area of the square on the hypotenuse ( c ).

  6. Pythagorean theorem - Wikipedia

    en.wikipedia.org/wiki/Pythagorean_theorem

    In mathematics, the Pythagorean theorem or Pythagoras' theorem is a fundamental relation in Euclidean geometry between the three sides of a right triangle.It states that the area of the square whose side is the hypotenuse (the side opposite the right angle) is equal to the sum of the areas of the squares on the other two sides.

  7. Square - Wikipedia

    en.wikipedia.org/wiki/Square

    All four internal angles of a square are equal (each being 90°, a right angle). [4] [5] The central angle of a square is equal to 90°. [4] The external angle of a square is equal to 90°. [4] The diagonals of a square are equal and bisect each other, meeting at 90°. [5] The diagonals of a square bisect its internal angles, forming adjacent ...

  8. Solid angle - Wikipedia

    en.wikipedia.org/wiki/Solid_angle

    The solid angle of a sphere measured from any point in its interior is 4 π sr. The solid angle subtended at the center of a cube by one of its faces is one-sixth of that, or 2 π /3 sr. The solid angle subtended at the corner of a cube (an octant) or spanned by a spherical octant is π /2 sr, one-eight of the solid angle of a sphere. [1]

  9. Quadrilateral - Wikipedia

    en.wikipedia.org/wiki/Quadrilateral

    Internal angle : 90° (for square and rectangle) ... This is a special case of the n-gon interior angle sum formula: S = (n − 2) ... It has the following properties: