Math Problem Statement
A man standing 5 feet away from the base of a lamppost casts a 3 feet long shadow. If he is 6 feet tall and walks away from the lamppost at a speed of 400 feet per minute, at what rate will his shadow lengthen ? In the figure, x represents the distance of the man from the bottom of the lamppost at time t, y represents the length of the man’s shadow at time t, and H represents the height of the lamppost.
Solution
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Math Problem Analysis
Mathematical Concepts
Related Rates
Similar Triangles
Derivatives
Formulas
H / (x + y) = 6 / y
y = 6x / (H - 6)
dy/dt = (6 / (H - 6)) * dx/dt
Theorems
Similar Triangles Theorem
Suitable Grade Level
Grades 11-12
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