Porisma
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Vectors: planes, normals and distances

Compare two planes · Diagrams

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Plane angles from acute or obtuse normal angles

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Two cross-sections show the same pair of intersecting planes and their perpendicular normals. With an acute normal angle theta, the plane angle alpha equals theta. Reversing one normal makes theta obtuse and alpha=pi−theta. Supplementary/equal angles give the absolute dot-product cosine formula.
Two cross-sections show the same pair of intersecting planes and their perpendicular normals. With an acute normal angle theta, the plane angle alpha equals theta. Reversing one normal makes theta obtuse and alpha=pi−theta. Supplementary/equal angles give the absolute dot-product cosine formula.
Two cross-sections show the same pair of intersecting planes and their perpendicular normals. With an acute normal angle theta, the plane angle alpha equals theta. Reversing one normal makes theta obtuse and alpha=pi−theta. Supplementary/equal angles give the absolute dot-product cosine formula.
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