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Find integral: int(x+2)/(x^(3)+27)dx

Find integral: x+2x3+27dx\int \frac{x+2}{x^{3}+27}\,dx

Full solution

Q. Find integral: x+2x3+27dx\int \frac{x+2}{x^{3}+27}\,dx
  1. Recognize and Decompose: Recognize the integral as a rational function and attempt to decompose it into partial fractions.\newlineWe have the integral:\newlinex+2x3+27dx\int\frac{x+2}{x^3+27}\,dx\newlineThe denominator can be factored as a sum of cubes:\newlinex3+27=(x+3)(x23x+9)x^3 + 27 = (x + 3)(x^2 - 3x + 9)\newlineWe will attempt to decompose the integrand into partial fractions.
  2. Set up Partial Fractions: Set up the partial fraction decomposition.\newlineWe express (x+2)/(x3+27)(x+2)/(x^3+27) as A/(x+3)A/(x+3) + (Bx+C)/(x23x+9)(Bx+C)/(x^2-3x+9), where AA, BB, and CC are constants to be determined.\newline(x+2)/(x3+27)=A/(x+3)+(Bx+C)/(x23x+9)(x+2)/(x^3+27) = A/(x+3) + (Bx+C)/(x^2-3x+9)\newlineMultiply both sides by the denominator (x3+27)(x^3+27) to clear the fractions:\newlinex+2=A(x23x+9)+(Bx+C)(x+3)x+2 = A(x^2-3x+9) + (Bx+C)(x+3)
  3. Solve for Constants: Solve for the constants AA, BB, and CC. We will now expand the right side and collect like terms to equate the coefficients on both sides of the equation. x+2=Ax23Ax+9A+Bx2+3Cx+Bx+3Cx+2 = Ax^2 - 3Ax + 9A + Bx^2 + 3Cx + Bx + 3C Combine like terms: x+2=(A+B)x2+(3A+B+3C)x+(9A+3C)x+2 = (A+B)x^2 + (-3A+B+3C)x + (9A+3C) Now we equate the coefficients of the corresponding powers of xx on both sides of the equation: For x2x^2: A+B=0A+B = 0 For xx: 3A+B+3C=1-3A+B+3C = 1 For the constant term: BB00
  4. Solve System of Equations: Solve the system of equations for AA, BB, and CC. From the x2x^2 term: A+B=0A+B = 0, so B=AB = -A. Substitute B=AB = -A into the equation for the xx term: 3AA+3C=1-3A - A + 3C = 1 4A+3C=1-4A + 3C = 1 Now we have two equations: 11) 4A+3C=1-4A + 3C = 1 22) BB11 We can solve this system of equations using substitution or elimination.
  5. Correct Calculation Mistake: Solve the system of equations using elimination.\newlineMultiply the first equation by 33 and the second equation by 44 to eliminate CC:\newline11) 12A+9C=3-12A + 9C = 3\newline22) 36A+12C=836A + 12C = 8\newlineNow add the two equations:\newline12A+9C+36A+12C=3+8-12A + 9C + 36A + 12C = 3 + 8\newline24A+21C=1124A + 21C = 11\newlineSince we have only one equation with two variables, we realize there is a mistake in our calculations. We need to correct this before proceeding.