Recognize and Decompose: Recognize the integral as a rational function and attempt to decompose it into partial fractions.We have the integral:∫x3+27x+2dxThe denominator can be factored as a sum of cubes:x3+27=(x+3)(x2−3x+9)We will attempt to decompose the integrand into partial fractions.
Set up Partial Fractions: Set up the partial fraction decomposition.We express (x+2)/(x3+27) as A/(x+3) + (Bx+C)/(x2−3x+9), where A, B, and C are constants to be determined.(x+2)/(x3+27)=A/(x+3)+(Bx+C)/(x2−3x+9)Multiply both sides by the denominator (x3+27) to clear the fractions:x+2=A(x2−3x+9)+(Bx+C)(x+3)
Solve for Constants: Solve for the constants A, B, and C. We will now expand the right side and collect like terms to equate the coefficients on both sides of the equation. x+2=Ax2−3Ax+9A+Bx2+3Cx+Bx+3C Combine like terms: x+2=(A+B)x2+(−3A+B+3C)x+(9A+3C) Now we equate the coefficients of the corresponding powers of x on both sides of the equation: For x2: A+B=0 For x: −3A+B+3C=1 For the constant term: B0
Solve System of Equations: Solve the system of equations for A, B, and C. From the x2 term: A+B=0, so B=−A. Substitute B=−A into the equation for the x term: −3A−A+3C=1−4A+3C=1 Now we have two equations: 1) −4A+3C=12) B1 We can solve this system of equations using substitution or elimination.
Correct Calculation Mistake: Solve the system of equations using elimination.Multiply the first equation by 3 and the second equation by 4 to eliminate C:1) −12A+9C=32) 36A+12C=8Now add the two equations:−12A+9C+36A+12C=3+824A+21C=11Since we have only one equation with two variables, we realize there is a mistake in our calculations. We need to correct this before proceeding.
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