Use Definitions 4.6 and 4.8 to prove that for any function f and interval [a,b], the trapezoid sum with n trapezoids is always the average of the left sum and the right sum with n rectangles.

Short Answer

Expert verified

It is provedthat for any function f and interval [a,b], the trapezoid sum with n trapezoids is always the average of the left sum and the right sum with n rectangles.

Step by step solution

01

Step 1. Given Information 

We are given thatfor any function f and interval [a,b], the trapezoid sum with n trapezoids is always the average of the left sum and the right sum with n rectangles.

02

Step 2. Proving the statement 

The left-sum defined for n rectangles on [a,b]is k=1nfxk-1Δx.

Where, Δx=b-an,xk=a+kΔx.

The right sum defined for n rectangles on [a,b]is k=1nfxkΔx.

The average of left sum and right sum is,

k=1nfxk-1Δx+k=1nfxkΔx2=k=1nfxk-1+fxk2Δx

The trapezoid sum for n rectangles on [a,b]is k=1nfxk-1+fxk2Δx.

Since f is increasing,

xk-1xk

Hence Proved.

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