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Two light sources of luminous intensitie...

Two light sources of luminous intensities P and 2P are placed 2 m apart on a horizontal line. The edge of a right dihedral formed two indentical opaque plates is placed on that line a distance x from the stronger source. At what inclination of the dihedral with the horizontal line will the edge be invisible?

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The correct Answer is:
`tanalpha=(x^(2))/(2(2-x)^(2))`
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