EASY - related rates question about rectangle area

Question

A rectangle has one side of 8 cm. How fast is the area of the rectangle changing at the instant when the other side is 18 cm and increasing at 2 cm per minute?

 

This is how I set it up:

 

dA/dt = L(dw/dt) + w(dL/dt)

0 = 18(dw/dt) + (8)(2)

 

I keep getting 0 cm^2/min as my answer which is obviously wrong

Answer 1

 

From the wording of the problem, it does not appear that the side of length 8 cm is changing!

 

Therefore A = 8x

dA/dt = 8 dy/dt and the given dy/dt is 2.

 

Therefore the desired dA/dt simply equals 16 cm/sec.

 

I suspect that your problem is not necessarily written exactly as it should have been!