Mathematics

Mathematics

Problem

A continuous function ff has average value 77 on [0,2][0,2]. Define g(x)=5f(4x)+Dg(x)=5f(4x)+D and consider gg on the interval [0,12][0,\tfrac12]. a. (i) Express the average value of gg on [0,12][0,\tfrac12] in terms of DD. b. (ii) Determine the value of DD for which the average value of gg on [0,12][0,\tfrac12] is 2020.
Intuitive explanation

The key is recognizing how a horizontal scaling and vertical shift transform both the domain and the average value. When you compress the input by a factor of 4 (via 4x4x), you're "speeding up" through the original function, but the average value of ff itself doesn't change—you're just sampling the same function values. The constant DD shifts all outputs uniformly, so it adds directly to the average. Set up the average value formula for gg on [0,12][0, \tfrac{1}{2}] and use the substitution u=4xu = 4x to connect it back to ff's known average on [0,2][0,2].

Intuitive explanation

The key is recognizing how a horizontal scaling and vertical shift transform both the domain and the average value. When you compress the input by a factor of 4 (via 4x4x), you're "speeding up" through the original function, but the average value of ff itself doesn't change—you're just sampling the same function values. The constant DD shifts all outputs uniformly, so it adds directly to the average. Set up the average value formula for gg on [0,12][0, \tfrac{1}{2}] and use the substitution u=4xu = 4x to connect it back to ff's known average on [0,2][0,2].

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