Approaching the Measure of a Set: Strategies for Finding f(Eα)

laurabon
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Homework Statement
let f : [a, b] → R ,
α ≥ 0 and Eα = {x ∈ [a, b] : exists f'(x) e |f'(x)|≤ α}
show that m (f(Eα)) ≤ α m(Eα)
Relevant Equations
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my question is how can I approch the problem ? And what is explicitly the set f(Eα)? {f(x) ∈ [a, b] such that what ??}
 
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Start with an arbitrary ##\epsilon \gt 0##. Use the definition of the (outer) measure of a set to find a countable set of open intervals, ##C_{epsilon}## covering ##E\alpha## where the summed length of the intervals is less than ##m( E\alpha) + \epsilon##. Use the definition of the derivative to find smaller intervals within each interval, ##I_n##, of ##C_{epsilon}## whose image, under ##f## is of length smaller than ##\alpha## length(##I_n##). Proceed from there.
 
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There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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