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MAT136H5 S 2025 - All Sections 3.4 Preparation Check
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Note: Example 3.29 as well as "the General Method" from the textbook Links to an external site. might help you with this question. Problem: Evaluate the integral ∫ x+4 (x+2)(x−4) dx A student hands in the following 'solution'. Is it correct? Line 1: Let's use the method of Partial Fractions. The degree of the numerator is less than the degree of the denominator, so we do not need to use long division. Line 2: There are two distinct (=different) linear factors so the partial fraction decomposition is of the form: Line 3: x+4 (x+2)(x−4) = A x+2 + B x−4 for some constants A and B. Line 4: Multiply both sides by (x+2)(x−4): Line 5: x+4=A(x−4)+B(x+2) Line 6: Simplify: x+4=Ax−4A+Bx+2B Line 7: The number of x on the two sides must be equal. Also, the constants on both sides must be equal: A+B=1 −4A+2B=4 Line 8: The first equation becomes B=1−A which can be inserted into the second equation: Line 9: −4A+2(1−A)=4⟹−4A+2−2A=4⟹−6A=2⟹A=− 1 3 Line 10: Therefore B=1−(− 1 3 )= 4 3 Line 11: Now we know the values of A and B so we can continue with the integral: Line 12: ∫ x+4 (x+2)(x−4) dx=∫( 4 3(x+2) − 1 3(x−4) )dx= Line 13: =∫ 4 3(x+2) dx−∫ 1 3(x−4) dx= Line 14: = 4 3 ln|x+2|− 1 3 ln|x−4|+C Is the solution correct, or if not, in which line does the first error occur? [line]
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Step-by-Step Analysis
The question asks us to evaluate the student’s partial fractions solution and identify where the first error occurs.
First, restating the problem: We need to integrate ∫ (x+4)/[(x+2)(x−4)] dx. The student proposes a partial fraction decomposition of the form (x+4)/[(x+2)(x−4)] = A/(x+2) + B/(x−4), then proceeds to solve for A and B.
Analyzing each step:
Line 1: The student states we will use partial fractions since the degree of the numerator (1) is less than the degree of the deno......Login to view full explanationLog in for full answers
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