Find the distance of the image behind the mirror....?

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miss1nik23

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An object that is 19 cm in front of a convex mirror has an image located 24 cm behind the mirror. How far behind the mirror is the image located when the object is 12 cm in front of the mirror?


PLEASE help me with this problem!

Everytime I do it I come up with a different answer. This is what I have been doing...

1/f = 1/19 + 1/-24 so f = 91.2

But, its a convex mirror, so doesnt f have to be negative? Im stuck after this part...
 
1/f=1/u+1/v <<note that the left hand side of the equation is a constant for any mirror.

Therefore, the two equations will be equal and you don't actually need to calculate the focal distance:

1/19+1/-24=1/f=1/12+1/d where d is the distance of the image.

Hence 1/19+1/-24=1/12+1/d

I'll let you reorganise the equation to find d.
 
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