A convex lens of focal length 80 cm and a concave lens of

A convex lens of focal length 80 cm and a concave lens of focal length 50 cm are combined together. What will be their resulting power?

We know that

1	=	1	+	1	; f₁ = 80 cm, f₂ = –50 cm
f		f₁		f₂

⇒ P =	1	= 1.25 - 2 = -0.75 D
	f