A -3.0 D lens is held 11.0 c m from an object 7.1 m m high. What is the image di

Question

                    A -3.0D lens is held                     11.0cm from an                     object 7.1mm                     high.                 

                    What is the image distance?                 

                    What is the height of the image?                 

                    Please show work. Answers I've been able to deduce have been -37 for the first one and 21.3 for the second and both are wrong. Thank you.                 

Explanation / Answer

1/f = -1/3

1/u = 1/0.11

1/v = 1/f - 1/u
1/v = -1/3- 1/0.11
1/v = 1/-0.11

Distance of image from the lens is v = -0.114 m
--------------------------------------...
Minus indicates virtual image.

Magnification m= v/u = -0.114/ 0.11 = -1.04

size is the larger as the object.
h = 1.04 x 7,1 = 7.37 mm

Minus sign indicates erect image.

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