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A pencil in projective geometry is a family of geometric objects with a common property, for example the set of lines that pass through a given point in a projective plane. More generally, a pencil is the special case of a linear system of divisors in which the parameter space is a projective line. Typical pencils of curves in the projective plane, for example, are written as :λ''C'' + μ''C''′ = 0 where :''C'' = 0, ''C''′ = 0 are plane curves. A pencil of planes, the family of planes through a given straight line, is sometimes referred to as a fan or a sheaf. ==See also== * Pencil beam * Pencil of circles * Lefschetz pencil * Matrix pencil 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pencil (mathematics)」の詳細全文を読む スポンサード リンク
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