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Answer:
The area of the rectangle is increasing at a rate of 168 square centimeters per second.
Step-by-step explanation:
Geometrically speaking, the area of a rectangle ([tex]A[/tex]), in square centimeters, is described by following expression:
[tex]A = w\cdot l[/tex] (1)
Where:
[tex]w[/tex] - Width, in centimeters.
[tex]h[/tex] - Height, in centimeters.
By Differential Calculus, we find an expression for the rate of change of the area of the rectangle ([tex]\dot A[/tex]), in square centimeters per second:
[tex]\dot A = \dot w\cdot l + w\cdot \dot l[/tex] (2)
Where:
[tex]\dot w[/tex] - Rate of change of the width of the rectangle, in centimeters per second.
[tex]\dot l[/tex] - Rate of change of the length of the rectangle, in centimeters per second.
If we know that [tex]w = 12\,cm[/tex], [tex]l = 15\,cm[/tex], [tex]\dot w = 4\,\frac{cm}{s}[/tex] and [tex]\dot l = 9\,\frac{cm}{s}[/tex], then the rate of change of the area of the rectangle is:
[tex]\dot A = \dot w\cdot l + w\cdot \dot l[/tex]
[tex]\dot A = 168\,\frac{cm^{2}}{s}[/tex]
The area of the rectangle is increasing at a rate of 168 square centimeters per second.