Lens maker's equation used correctly?

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The discussion revolves around the application of the lens maker's equation to find the image position for a thick double convex lens. The object is placed 60 cm from the lens, which has specific radii of curvature and a thickness of 2 cm. One participant calculated the image position as 40 cm, while the correct answer is 39.9 cm, indicating a need to account for the lens thickness in calculations. There is confusion about whether the thickness should be included in the lens maker's equation, as one method yielded an incorrect result of 40.9 cm. Ultimately, it is emphasized that the thickness must be considered for accurate results in such calculations.
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Homework Statement



An object is placed 60 cm from a thick double convex lens, with faces of radii of curvature 20 cm and 30 cm, with thickness of 2 cm, and index of refraction is 1.5. Find the position of the image. Ans: ( 39.9 cm)

Homework Equations



lens maker's equation, na/object + na/image = (nb - na)(1/R1 - 1/R2)

The Attempt at a Solution



I used this equation and got 40 cm, as opposed to 39.9. I figured it couldn't be a rounding error considering the numbers given. Am I supposed to use the 2 cm thickness somehow?
 
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When I calculated the answer, it came out to be 40.9 cm. Strange! I used the lensmaker equation given in Wikipedia. These were my results : f= 900/37 cm, u=-60 cm (given) So, using lens formula v = 40.9cm. And yes you need to use the thickness. See the lensmaker's equation in Wikipedia!
 
@Danny :the equation which you are using seems to be derived from thin lens equation where you neglect thickness as it's too small compared to Radii of curvature.
 

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