TheoremBase

Rules for the Riemann Integral: Sums, Scalar Multiples, Monotonicity, Bounds and Constants

The Riemann integral on a closed interval is additive and homogeneous, monotone, bounded by the bounds of the integrand times the length of the interval, and gives c(b-a) for the constant c.

Statement

In the setting of The Real Line: Standing Notation and Background for Calculus on Intervals, let a,b∈Ra,b\in\mathbb{R} with a<ba<b, let integrability on [a,b][a,b] and the integral ∫ab\int_{a}^{b} be as in The Riemann Integral on a Closed Interval via Lower and Upper Integrals, and let the sum f+gf+g and the scalar multiple cfcf of maps f,g:[a,b]→Rf,g:[a,b]\to\mathbb{R} and c∈Rc\in\mathbb{R} be as in Pointwise Operations on Real-Valued Maps (i), with I=[a,b]I=[a,b]. A map h:[a,b]→Rh:[a,b]\to\mathbb{R} is bounded if there is B∈RB\in\mathbb{R} with ∣h(t)∣≤B|h(t)|\le B for every t∈[a,b]t\in[a,b]. Let f,g:[a,b]→Rf,g:[a,b]\to\mathbb{R} be bounded maps that are integrable on [a,b][a,b], and let c∈Rc\in\mathbb{R}.

f+gf+g is bounded and integrable on [a,b][a,b], and ∫ab(f+g)=∫abf+∫abg\int_{a}^{b}(f+g)=\int_{a}^{b}f+\int_{a}^{b}g.

cfcf is bounded and integrable on [a,b][a,b], and ∫abcf=c∫abf\int_{a}^{b}cf=c\int_{a}^{b}f.

If f(t)≤g(t)f(t)\le g(t) for every t∈[a,b]t\in[a,b], then ∫abf≤∫abg\int_{a}^{b}f\le\int_{a}^{b}g.

If m,M∈Rm,M\in\mathbb{R} and m≤f(t)≤Mm\le f(t)\le M for every t∈[a,b]t\in[a,b], then m (b−a)≤∫abf≤M (b−a)m\,(b-a)\le\int_{a}^{b}f\le M\,(b-a).

If B∈RB\in\mathbb{R} and ∣f(t)∣≤B|f(t)|\le B for every t∈[a,b]t\in[a,b], then ∣∫abf∣≤B (b−a)\bigl|\int_{a}^{b}f\bigr|\le B\,(b-a).

The constant map [a,b]→R[a,b]\to\mathbb{R} with value cc is bounded and integrable on [a,b][a,b], and its integral is ∫abc dt=c (b−a)\int_{a}^{b}c\,dt=c\,(b-a).

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