A concave mirror of focal length ‘f1’ is placed at a

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A concave mirror of focal length ‘f₁’ is placed at a distance of 'd’ from a convex lens of focal length ‘f₂’. A beam of light coming from infinity and falling on this convex lens-concave mirror combination returns to infinity.The distance ‘d’ must equal :

1. f₁ + f₂
2. –f₁ + f₂
3. 2f₁ + f₂
4. –2f₁ + f₂

Correct Option: C

d = f₂ + 2f₁