Question

Find the dimensions of the rectangle with area 289 square inches that has minimum perimeter, and then find the minimum perimeter.

Answer 1

 To minimize the perimeter you should always have a square. 
sqrt(289) = 17 
The dimensions should be 17 X 17 

To see , try starting at length 1, and gradually increase the length. 
The height decreases at a faster rate than the length increases, up until you reach a square. 

Or if you want to use algebra, Say the width is 17-x 
Then the length is 289/(17-x) 

Now, this is bigger than 17+x, as shown here: 
289/(17-x) > 17+x 
289 > 289 - x^2 
which is true. 
so the perimeter would be bigger than 2 * (17- x + 17 + x) = 2 * (2 * 17) = 4 * 17 

Again, the dimensions should be a square. 17 X 17.