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PROBLEM

Find δ\delta such that if x1<δ|x-1|<\delta, then f(x)1<0.2|f(x)-1|<0.2, given f(1)=1f(1)=1, f(1.1)=0.8f(1.1)=0.8, f(1.2)=1.2f(1.2)=1.2.

STEP 1

Assumptions1. The function ff has a known point (1,1)(1,1).
. The function ff intersects the line y=0.8y=0.8 at x=1.1x=1.1.
3. The function ff intersects the line y=1.y=1. at x=1.x=1..
4. We need to find a number δ\delta such that if x1<δ|x-1|<\delta then f(x)1<0.|f(x)-1|<0..

STEP 2

We are given that f(x)f(x) intersects the lines y=0.8y=0.8 and y=1.2y=1.2 at x=1.1x=1.1 and x=1.2x=1.2 respectively. This means that f(1.1)=0.8f(1.1) =0.8 and f(1.2)=1.2f(1.2) =1.2.

STEP 3

We are looking for a δ\delta such that if x1<δ|x-1|<\delta then f(x)1<0.2|f(x)-1|<0.2. This means that the values of f(x)f(x) should lie between 0.80.8 and 1.21.2 when xx is in the interval (1δ,1+δ)(1-\delta,1+\delta).

STEP 4

Since f(1.1)=0.8f(1.1) =0.8 and f(1.2)=1.2f(1.2) =1.2, we can see that the values of f(x)f(x) lie between 0.80.8 and 1.21.2 when xx is in the interval (1.1,1.2)(1.1,1.2).

STEP 5

Therefore, we can choose δ\delta such that (1δ,1+δ)(1-\delta,1+\delta) is a subset of the interval (1.1,1.2)(1.1,1.2).

SOLUTION

The distance between 11 and 1.11.1 is 0.10.1 and the distance between 11 and 1.21.2 is 0.20.2. Therefore, we choose δ\delta to be the smaller of these two distances, which is 0.10.1.
So, δ=0.1\delta =0.1.
With this choice of δ\delta, if x1<δ|x-1|<\delta then f(x)1<0.2|f(x)-1|<0.2.

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