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  2. Tangent lines to circles - Wikipedia

    en.wikipedia.org/wiki/Tangent_lines_to_circles

    In Euclidean plane geometry, a tangent line to a circle is a line that touches the circle at exactly one point, never entering the circle's interior. Tangent lines to circles form the subject of several theorems, and play an important role in many geometrical constructions and proofs. Since the tangent line to a circle at a point P is ...

  3. Tangent - Wikipedia

    en.wikipedia.org/wiki/Tangent

    Tangent line to a space curve. In mathematics, a tangent vector is a vector that is tangent to a curve or surface at a given point. Tangent vectors are described in the differential geometry of curves in the context of curves in R n. More generally, tangent vectors are elements of a tangent space of a differentiable manifold.

  4. Descartes' theorem - Wikipedia

    en.wikipedia.org/wiki/Descartes'_theorem

    In geometry, Descartes' theorem states that for every four kissing, or mutually tangent, circles, the radii of the circles satisfy a certain quadratic equation. By solving this equation, one can construct a fourth circle tangent to three given, mutually tangent circles. The theorem is named after René Descartes, who stated it in 1643.

  5. Circle - Wikipedia

    en.wikipedia.org/wiki/Circle

    The tangent line through a point P on the circle is perpendicular to the diameter passing through P. If P = (x 1, y 1) and the circle has centre (a, b) and radius r, then the tangent line is perpendicular to the line from (a, b) to (x 1, y 1), so it has the form (x 1 − a)x + (y 1 – b)y = c.

  6. Parabola - Wikipedia

    en.wikipedia.org/wiki/Parabola

    The parabola is the locus of points in that plane that are equidistant from the directrix and the focus. Another description of a parabola is as a conic section, created from the intersection of a right circular conical surface and a plane parallel to another plane that is tangential to the conical surface. [a]

  7. Tangent half-angle formula - Wikipedia

    en.wikipedia.org/wiki/Tangent_half-angle_formula

    The angle between the horizontal line and the shown diagonal is ⁠ 1 2 ⁠ (a + b). This is a geometric way to prove the particular tangent half-angle formula that says tan ⁠ 1 2 ⁠ (a + b) = (sin a + sin b) / (cos a + cos b). The formulae sin ⁠ 1 2 ⁠(a + b) and cos ⁠ 1 2 ⁠(a + b) are the ratios of the actual distances to the length ...

  8. Elliptic curve - Wikipedia

    en.wikipedia.org/wiki/Elliptic_curve

    This equation is not defined on the line at infinity, but we can multiply by to get one that is : Z Y 2 = X 3 + a Z 2 X + b Z 3 {\displaystyle ZY^{2}=X^{3}+aZ^{2}X+bZ^{3}} This resulting equation is defined on the whole projective plane, and the curve it defines projects onto the elliptic curve of interest.

  9. Law of tangents - Wikipedia

    en.wikipedia.org/wiki/Law_of_tangents

    Fourier. v. t. e. In trigonometry, the law of tangents or tangent rule[1] is a statement about the relationship between the tangents of two angles of a triangle and the lengths of the opposing sides. In Figure 1, a, b, and c are the lengths of the three sides of the triangle, and α, β, and γ are the angles opposite those three respective sides.