Definite Integration
Properties of Definite Integrals
Grade 12
Question:
<p>Suppose that a continuous function \(f(x)\) satisfies the relation \(\int_{x}^{x+1} f(t)\, dt = e^x\) for every \(x \geq 0\). The value of \(f(2) - f(0)\), equals:</p>
<p>(a) 1</p>
<p>(b) \(e - 1\)</p>
<p>(c) \(e + 1\)</p>
<p>(d) \(e^2 + 1\)</p>
Step-by-Step Solution
Key Concept: Differentiate both sides of the integral equation with respect to x using Leibniz rule to convert the functional equation into a differential equation that f must satisfy.
<p><strong>Step 1:</strong> Differentiate both sides of $\int_{x}^{x+1} f(t)\,dt = e^x$ with respect to $x$ using Leibniz rule:</p><p>$$\frac{d}{dx}\int_{x}^{x+1} f(t)\,dt = \frac{d}{dx}(e^x)$$</p><p><strong>Step 2:</strong> Apply Leibniz rule: $\frac{d}{dx}\int_{a(x)}^{b(x)} f(t)\,dt = f(b(x))\cdot b'(x) - f(a(x))\cdot a'(x)$</p><p>$$f(x+1)\cdot(1) - f(x)\cdot(1) = e^x$$</p><p>$$f(x+1) - f(x) = e^x$$</p><p><strong>Step 3:</strong> Use this relation for specific values. For $x = 0$: $f(1) - f(0) = e^0 = 1$</p><p>For $x = 1$: $f(2) - f(1) = e^1 = e$</p><p><strong>Step 4:</strong> Add these equations:</p><p>$$[f(1) - f(0)] + [f(2) - f(1)] = 1 + e$$</p><p>$$f(2) - f(0) = 1 + e$$</p><p>∴ Answer: B</p>
Correct Answer: B