Question Bank • QB_DIAG_S1_002 NAT • 2 Marks

Section 1: Engineering Mathematics

Calculus

Subtopic: Double and triple integrals

Question Statement:

Referring to the shaded bounded region $R$ shown in the accompanying figure, bounded between the parabola $y = x^2$ and the straight line $y = 2x$ intersecting at $(0,0)$ and $(2,4)$, the area of region $R$ evaluated via double integration $\iint_R dx \, dy$ is ________ (round off to two decimal places).

Answer Key:

1.33

Step-by-Step Solution & Explanation

1. Points of intersection: $x^2 = 2x \implies x(x - 2) = 0 \implies x = 0, x = 2$ 2. In region $R$, for any $x \in [0, 2]$, the upper curve is $y = 2x$ and lower curve is $y = x^2$. 3. Area via double integral: $A = \int_{0}^{2} \int_{x^2}^{2x} dy \, dx = \int_{0}^{2} (2x - x^2) \, dx = \left[ x^2 - \frac{x^3}{3} \right]_0^2 = 4 - \frac{8}{3} = \frac{4}{3} \approx 1.33$.
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