\section*Intermediate Problems
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\subsection*Problem 1 Compute the Riemann sum for ( f(x) = x^2 ) on ([0,2]) using 4 subintervals and right endpoints.
\subsection*Solution 4 Let (u=x^2), (du=2x,dx) (\Rightarrow) (x,dx = du/2). When (x=0,u=0); (x=1,u=1). [ \int_0^1 x e^x^2dx = \frac12\int_0^1 e^u du = \frac12(e-1). ] riemann integral problems and solutions pdf
\beginenumerate[label=\arabic*.] \item (\int_0^1 (3x^2-2x+1)dx = 1) \item (\int_1^e \frac1xdx = 1) \item (\int_0^\pi/2 \sin 2x,dx = 1) \item (\int_0^4 |x-2|dx = 4) \item (\lim_n\to\infty \sum_k=1^n \fracnn^2+k^2 = \frac\pi4) \endenumerate
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(1/π)[sin x]₀^π = 0. Advanced Problems Problem 7 Prove limit definition for continuous f. [ \int_0^1 x e^x^2dx = \frac12\int_0^1 e^u du = \frac12(e-1)
0 ≤ sin x ≤ 1 and 1 ≤ 1+x² ≤ 1+(π/2)², but simpler: 0 ≤ f(x) ≤ 1 ⇒ 0 ≤ I ≤ π/2. Lower bound π/6 comes from sin x ≥ 2x/π? Accept as given.
Standard Riemann sum definition; continuity ensures integrability.
Evaluate ∫₀³ (2x+1) dx using the definition of the Riemann integral. Advanced Problems Problem 7 Prove limit definition for
\subsection*Solution 5 For (x\in[0,\pi/2]), (0 \le \sin x \le 1) and (1 \le 1+x^2 \le 1+(\pi/2)^2 \approx 3.467). So [ \frac\sin x1+x^2 \ge 0,\quad \frac\sin x1+x^2 \le 1. ] Integrating: (\int_0^\pi/2 0,dx =0) (lower bound), but a better lower bound: (\sin x \ge \frac2x\pi)? Actually simpler: (\sin x \ge 2x/\pi)? Let's do: Lower bound: (\sin x \ge \frac2\pix)? Not sharp. But we can note: (\frac\sin x1+x^2 \ge \frac\sin x1+(\pi/2)^2 \ge ?) Better: known inequality: (\frac2\pix \le \sin x \le x) on ([0,\pi/2]). Then: [ \int_0^\pi/2 \frac2x/\pi1+(\pi/2)^2 dx \le \int_0^\pi/2 \frac\sin x1+x^2dx \le \int_0^\pi/2 x,dx. ] Compute: (\int_0^\pi/2 x dx = \pi^2/8 \approx 1.23) but (\pi/2 \approx 1.57), so upper bound (\pi/2) is trivial. Actually simpler: (\sin x \le 1) gives (\int_0^\pi/2 \frac11+x^2dx = \arctan(\pi/2) \approx 1.0). But problem says (\pi/2)? Let's check: (\pi/2 \approx 1.57) which is larger, so it's correct. Lower bound: (\sin x \ge 0) gives 0, but they want (\pi/6\approx0.523). To get (\pi/6), use (\sin x \ge 2x/\pi): (\int_0^\pi/2 \frac2x/\pi1+(\pi/2)^2 dx)? That yields something else. But given the problem statement, we accept the trivial bounds: (0 \le f(x) \le 1) gives (0 \le \int \le \pi/2). But they wrote (\pi/6) as lower bound — perhaps using (\sin x \ge x/2)? Anyway, the idea: use (m \le f(x) \le M \Rightarrow m(b-a) \le \int_a^b f \le M(b-a)).
\subsection*Problem 9 Suppose (f) is Riemann integrable on ([a,b]) and (f(x) \ge 0) for all (x). Prove (\int_a^b f \ge 0).
