Answer:
the focal length of the mirror is : 
Explanation:
Use the formula for the formation of image using a divergent mirror and recalling that the image (s') that this mirror formed is virtual, so it is entered as a negative number in the formula. Use the object position (s) as 10, the image position (s') as -2, and derive the value of the focal length:

a fixed luminous point in the night sky which is a large, remote incandescent body like the sun. or a conventional or stylized representation of a star, typically one having five or more points.
Answer:
The illumination on the book before the lamp is moved is 9 times the illumination after the lamp is moved.
Explanation:
The distance of the book before the lamp is moved, 
The distance of the book after the lamp is moved, 
Illumination can be given by the formula, 
Illumination before the lamp is moved, 
Illumination after the lamp is moved, 



The illumination on the book before the lamp is moved is 9 times the illumination after the lamp is moved.
Answer:
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