Math Problem Statement

Calculate the limit for the function 𝑓(π‘₯)=(15/2)π‘₯+4f(x)=152x+4 over the interval [0,4].[0,4]. Verify your answer by using geometry.

(Give your answer as a whole or exact number.) limπ‘β†’βˆžπΏπ‘=limNβ†’βˆžLN=

Solution

To calculate the limit and verify using geometry, let’s analyze the problem step-by-step.

Function:

f(x)=152x+4f(x) = \frac{15}{2}x + 4 The interval is [0,4][0,4]. We are tasked with finding:

lim⁑Nβ†’βˆžLN\lim_{N \to \infty} L_N where LNL_N represents the Riemann sum approximation of the definite integral over [0,4][0,4].

Step 1: Calculate the exact integral of f(x)f(x) over [0,4][0,4]

The definite integral of f(x)f(x) from 0 to 4 is:

∫04f(x) dx=∫04(152x+4) dx\int_0^4 f(x) \, dx = \int_0^4 \left(\frac{15}{2}x + 4\right) \, dx

Breaking this into two parts:

∫04152x dx+∫044 dx\int_0^4 \frac{15}{2}x \, dx + \int_0^4 4 \, dx

First term:

∫04152x dx=152∫04x dx=152β‹…[x22]04=152β‹…162=152β‹…8=60\int_0^4 \frac{15}{2}x \, dx = \frac{15}{2} \int_0^4 x \, dx = \frac{15}{2} \cdot \left[\frac{x^2}{2}\right]_0^4 = \frac{15}{2} \cdot \frac{16}{2} = \frac{15}{2} \cdot 8 = 60

Second term:

∫044 dx=4β‹…βˆ«041 dx=4β‹…[x]04=4β‹…(4βˆ’0)=16\int_0^4 4 \, dx = 4 \cdot \int_0^4 1 \, dx = 4 \cdot \left[x\right]_0^4 = 4 \cdot (4 - 0) = 16

Total integral:

∫04f(x) dx=60+16=76\int_0^4 f(x) \, dx = 60 + 16 = 76

Thus, the exact value of lim⁑Nβ†’βˆžLN\lim_{N \to \infty} L_N is: 76\boxed{76}

Step 2: Verify using geometry

The graph of f(x)f(x) is a straight line, so the area under the curve from x=0x = 0 to x=4x = 4 can be verified geometrically.

  1. Trapezoid Approach: Divide the area into a trapezoid with parallel sides f(0)f(0) and f(4)f(4), and height 4.
    • f(0)=152(0)+4=4f(0) = \frac{15}{2}(0) + 4 = 4
    • f(4)=152(4)+4=30+4=34f(4) = \frac{15}{2}(4) + 4 = 30 + 4 = 34
    • Trapezoid area: Area=12β‹…heightβ‹…(base1+base2)\text{Area} = \frac{1}{2} \cdot \text{height} \cdot (\text{base}_1 + \text{base}_2) Area=12β‹…4β‹…(4+34)=2β‹…38=76\text{Area} = \frac{1}{2} \cdot 4 \cdot (4 + 34) = 2 \cdot 38 = 76

Thus, the geometric verification confirms the result: 76\boxed{76}

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Math Problem Analysis

Mathematical Concepts

Calculus
Definite Integrals
Riemann Sums
Geometric Verification

Formulas

Definite integral formula: ∫[a, b] f(x) dx
Area of a trapezoid: (1/2) Γ— height Γ— (base1 + base2)

Theorems

Fundamental Theorem of Calculus

Suitable Grade Level

Grades 11-12 or early college