The length of a rectangle is increasing at a rate of 8 cm / s and its width is
increasing at a rate of 3 cm / s. When the length (x) is 20 cm and the width (y) is 10 cm, how
fast is the area of the rectangle increasing?
And what will be the area (A) of rectangle after 2 s?
The first part of the question can be solved as :
In the second part of the question, I confused because I got two different results:
First result I got area=576 cm^2
Second result I got area=480 cm^2
So, which answer is the correct one ?
Best Answer
Your first result is correct. It is given (or at least strongly implied) that the sides of the rectangle are growing at a constant rate. Your second attempt is assuming that the area is also growing at a constant rate, but that isn't true. To check, you can calculate how fast the area of the rectangle is growing at 2 seconds by feeding that new info into the equation you came up with in the first part.