Posted by Amy on .
The height of a triangle is increasing at a rate of 1 cm/min while the area of the triangle is increasing at a rate of 2 square cm/min. At what rate is the base of the triangle changing when the height is 7 centimeters and the area is 91 square centimeters?

Calculus Practice Problems 
Reiny,
A = (1/2) b h
dA/dt = (1/2)(b dh/dt + h db/dt)
given: dA/dt = 2 , dh/dt = 1 , A = 91 , h = 7 ,
we need the base b,
from A = 1/2)bh
91 = (1/2)(7b)
182 = 7b
b = 26
2 = (1/2)(26(1) + 7db/dt)
4 = 23 + 7db/dt
db/dt = 19/7 cm/min
At that moment, the base is decreasing at 19/7 cm/min