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The base of a triangle is decreasing at a rate of 13 millimeters per minute and the height of the triangle is increasing at a rate of 6 millimeters per minute.
At a certain instant, the base is 5 millimeters and the height is 1 millimeter.
What is the rate of change of the area of the triangle at that instant (in square millimeters per minute)?
Choose 1 answer:
(A) 21.5
(B) -8.5
(C) -21.5
(D) 8.5

The base of a triangle is decreasing at a rate of 1313 millimeters per minute and the height of the triangle is increasing at a rate of 66 millimeters per minute.\newlineAt a certain instant, the base is 55 millimeters and the height is 11 millimeter.\newlineWhat is the rate of change of the area of the triangle at that instant (in square millimeters per minute)?\newlineChoose 11 answer:\newline(A) 2121.55\newline(B) 8-8.55\newline(C) 21-21.55\newline(D) 88.55

Full solution

Q. The base of a triangle is decreasing at a rate of 1313 millimeters per minute and the height of the triangle is increasing at a rate of 66 millimeters per minute.\newlineAt a certain instant, the base is 55 millimeters and the height is 11 millimeter.\newlineWhat is the rate of change of the area of the triangle at that instant (in square millimeters per minute)?\newlineChoose 11 answer:\newline(A) 2121.55\newline(B) 8-8.55\newline(C) 21-21.55\newline(D) 88.55
  1. Calculate Initial Area: Now, let's calculate the initial area of the triangle with the given base and height.\newlineArea = (5mm×1mm)/2=52mm2=2.5mm2(5 \, \text{mm} \times 1 \, \text{mm}) / 2 = \frac{5}{2} \, \text{mm}^2 = 2.5 \, \text{mm}^2.
  2. Find Rate of Change: To find the rate of change of the area, we'll use the formula for the derivative of the area with respect to time, dAdt=12×(dbdt×h+b×dhdt)\frac{dA}{dt} = \frac{1}{2} \times (\frac{db}{dt} \times h + b \times \frac{dh}{dt}), where dbdt\frac{db}{dt} is the rate of change of the base and dhdt\frac{dh}{dt} is the rate of change of the height.
  3. Plug in Values: We know dbdt=13mm/min\frac{db}{dt} = -13 \, \text{mm/min} (since the base is decreasing) and dhdt=6mm/min\frac{dh}{dt} = 6 \, \text{mm/min} (since the height is increasing). Let's plug these values into the formula. dAdt=12×(13mm/min×1mm+5mm×6mm/min)\frac{dA}{dt} = \frac{1}{2} \times (-13 \, \text{mm/min} \times 1 \, \text{mm} + 5 \, \text{mm} \times 6 \, \text{mm/min}).
  4. Perform Calculation: Now, let's do the calculation.\newlinedAdt=12(13mm2/min+30mm2/min)=1217mm2/min=8.5mm2/min\frac{dA}{dt} = \frac{1}{2} * (-13 \, \text{mm}^2/\text{min} + 30 \, \text{mm}^2/\text{min}) = \frac{1}{2} * 17 \, \text{mm}^2/\text{min} = 8.5 \, \text{mm}^2/\text{min}.

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