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Ch. 6 - Applications of Integration
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 6, Problema 6.6.15

Find the area of the surface generated when the given curve is revolved about the given axis.


y=4x−1, for 1≤x≤4; about the y-axis (Hint: Integrate with respect to y.)

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Step 1: Recall the formula for the surface area of a curve revolved about the y-axis. The formula is: A = 2π ∫ x √(1 + (dx/dy)²) dy, where x is expressed as a function of y.
Step 2: Rewrite the given equation y = 4x - 1 to express x in terms of y. Solve for x: x = (y + 1)/4.
Step 3: Compute dx/dy by differentiating x = (y + 1)/4 with respect to y. The derivative is: dx/dy = 1/4.
Step 4: Determine the limits of integration for y. Since the curve is defined for 1 ≤ x ≤ 4, substitute these x-values into the equation y = 4x - 1 to find the corresponding y-values. For x = 1, y = 3; for x = 4, y = 15. Thus, the limits of integration are 3 ≤ y ≤ 15.
Step 5: Substitute x = (y + 1)/4 and dx/dy = 1/4 into the surface area formula. The integral becomes: A = 2π ∫315 ((y + 1)/4) √(1 + (1/4)²) dy. Simplify the expression inside the integral and proceed to evaluate the integral.

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