Question

As the zoom lens in a camera moves in & out, the size of the rectangular image changes. If the current image is 8cm x 6cm, find the rate at which the area of the img is changing (dA/df) if the length of the image is changing at 0.5cm/s and width changing at 0.1cm/s

Answer 1

Area = LW ; dL/dt = .5; dW/dt = .1

Answer 2

dA/dt = dA/dL dL/dt

or

dA/dt = dA/dW dW/dt

Answer 3

dA/dt = L dW/dt + W dL/dt might be better :)

Answer 4

dA/dt = L dW/dt + W dL/dt

is 8 the length or the width?

dA/dt = L dW/dt + W dL/dt

Answer 5

if length we do this:

dA/dt = 8* .1 + 6 * .5

A' = .8 + 3.0 = 3.8 cm^2/sec

Answer 6

thanks alot