Question

F=20см=0,2м d=40см=0,4 f-?

Answer 1

По формуле тонкой линзы:
1/F = 1/d + 1/f

1/f = 1/F - 1/d

1/f = 1/0,2 - 1/0,4 = 10/4 = 5/2

f = 2/5 = 0,4 м

Answer 2

It looks like you're trying to find the focal length (f) of a lens or mirror using the formula relating object distance (F) and image distance (d) to the focal length. The formula is:

1/f = 1/F + 1/d

Given: F = 0.2 meters (20 cm) d = 0.4 meters (40 cm)

Now, let's plug these values into the formula to find the focal length (f):

1/f = 1/0.2 + 1/0.4

To add the fractions, you need to find a common denominator, which is 0.4 in this case:

1/f = (0.4 + 1) / 0.4

1/f = 1.4 / 0.4

Now, invert both sides of the equation to solve for f:

f = 0.4 / 1.4

f ≈ 0.2857 meters

So, the focal length (f) is approximately 0.2857 meters or 28.57 centimeters.