Question

The length of a rectangle is increasing at a rate of 6 cm/s and its width is increasing at a rate of 5 cm/s. when the length is 15 cm and the width is 9 cm, how fast is the area of the rectangle increasing?

Answer 1

By definition, the area of a rectangle is given by:
A = w * l
Where,
w: width
l: long
Deriving this expression we have:
A '= w' * l + w * l '
Substituting the values:
A '= (5) * (15) + (9) * (6)
A '= 129 cm ^ 2 / s
Answer:
The area of the rectangle is increasing at:
A '= 129 cm ^ 2 / s