You are trying to photograph a bird sitting on a tree branch

You are trying to photograph a bird sitting on a tree branch, but a tall hedge is blocking your view. However, as the drawing shows, a plane mirror reflects light from the bird into your camera. For what distance must you set the focus of the camera lens in order to snap a sharp picture of the bird\'s image?

Solution

tan theta = [4.3 - y₁ / 2.1] = [y₁ / 3.7]

(4.3 * 3.7) - 3.7 y₁ = 2.1 y₁

15.91 = 2.1 y₁ + 3.7 y₁

y₁ = 2.74 m

distance = sqrt [y₁² + 3.7²] + sqrt[(4.3 - 2.74)² - 2.1²]

= 7.2 m