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Ch. 8 - Integration Techniques
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 8, Problema 8.3.68

67-70. Integrals of the form ∫ sin(mx)cos(nx) dx Use the following product-to-sum identities to evaluate the given integrals:
sin(mx)sin(nx) = ½[cos((m-n)x) - cos((m+n)x)]
sin(mx)cos(nx) = ½[sin((m-n)x) + sin((m+n)x)]
cos(mx)cos(nx) = ½[cos((m-n)x) + cos((m+n)x)]
68. ∫ sin(5x)sin(7x) dx

Guida verificata passo dopo passo
1
Step 1: Recognize that the integral involves the product of two sine functions, sin(5x) and sin(7x). To simplify this, use the product-to-sum identity for sin(mx)sin(nx): sin(mx)sin(nx) = ½[cos((m-n)x) - cos((m+n)x)].
Step 2: Substitute m = 5 and n = 7 into the identity. This gives sin(5x)sin(7x) = ½[cos((5-7)x) - cos((5+7)x)]. Simplify the expressions inside the cosine functions: (5-7)x = -2x and (5+7)x = 12x.
Step 3: Rewrite the integral using the product-to-sum identity: ∫ sin(5x)sin(7x) dx = ½ ∫ [cos(-2x) - cos(12x)] dx. Note that cos(-2x) = cos(2x) because cosine is an even function.
Step 4: Break the integral into two separate integrals: ∫ sin(5x)sin(7x) dx = ½ [∫ cos(2x) dx - ∫ cos(12x) dx].
Step 5: Integrate each term separately. Recall that the integral of cos(kx) is (1/k)sin(kx) + C, where k is a constant. Apply this formula to both ∫ cos(2x) dx and ∫ cos(12x) dx, and combine the results to complete the solution.

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Product-to-Sum Identities

Product-to-sum identities are trigonometric formulas that express products of sine and cosine functions as sums or differences of sine and cosine functions. These identities simplify the integration of products of trigonometric functions by transforming them into a more manageable form, making it easier to evaluate integrals.
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Integration techniques refer to various methods used to compute integrals, including substitution, integration by parts, and the use of trigonometric identities. In the context of the given question, applying product-to-sum identities is a specific technique that allows for the simplification of integrals involving products of sine and cosine functions.
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