If projections of three points A, B, C on a given plane are A′,B′,C′ ; then ΔA′B′C′=cosθ(ΔABC) , w

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Q 1277134086.     If projections of three points A, B, C on a given plane are A′,B′,C′ ; then ΔA′B′C′=cosθ(ΔABC) , where θ is the angle between the planes ABC and ′B′C′ . In general, if A_0 is the area of any plane curve and A is the area of its projection on any plane, then A=cosθA_0

Suppose AB is a diameter of a circle and P is a plane through AB making an angle θ with the plane of the circle. If diameter of the circle is 2a, then the eccentricity of the curve of projection of the circle on P is
A

sin θ

B

(2asinθ)/(1+a)

C

(2acosθ)/(1+a)

D

cos θ

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