URDANETA CITY UNIVERSITY College of Engineering and Architecture Owned and Operated by the City Government of Urdaneta THE INDEFINITE INTEGRAL We shall begin our study of the inverse of differentiation. We have learned in differential calculus that differentiation is the process of finding the derivative or differential of a given function. This time, we reverse the process, that is, we find the function whose derivative or differential is given. The inverse of differentiation is called antidifferentiation or integration. OBJECTIVES. At the end, the student should be able to: 1. Know the concept of the indefinite integral. 2. Apply the basic integration formulas. The symbol ∫ is used to denote the process of integration. The integral of 4π₯ 3 is π₯ 4 + πΆ can be expressed symbolically as ∫ 4π₯ 3 ππ₯ = π₯ 4 + πΆ The expression ∫ 4π₯ 3 ππ₯ is called an indefinite integral. Generally, the indefinite integral of a function f(x) is denoted by ∫ π(π₯)ππ₯ and defined as follows ∫ π(π₯)ππ₯ = πΉ(π₯) + πΆ if ππΉ(π₯) = π(π₯)ππ₯ … πΈππ (1.1) We call the symbol ∫ the integral sign, f(x) the integrand, C the arbitrary constant of integration, and F(x) + C the value of the indefinite integral ∫ π(π₯)ππ₯. The differential dx indicates that x is the variable of integration. 1.1 The Indefinite Integral We know that by differentiation, a derivative or differential is obtained from a given function. Suppose the derivative (or differential) of a function is given, how can a function be found? For example, what function has for its derivative 4π₯ 3 or for its differential 4π₯ 3 ππ₯? We π know that (π₯ 4 ) = 4π₯ 3 or π(π₯ 4 ) = 4π₯ 3 ππ₯. Thus, the answer to the question above is π₯ 4 . ππ₯ However, that is not the only possible answer. We may also give the following functions as valid answers: π₯4 − 3 π₯ 4 + 15 π₯4 + 8 Table below illustrate further the integral concept: DIFFERENTIAL INTEGRAL π(π₯ 6 ) = 6π₯ 5 ππ₯ ∫ 6π₯ 5 ππ₯ = π₯ 6 + πΆ π(π₯) = ππ₯ ∫ ππ₯ = π₯ + πΆ π(π π₯ ) = π π₯ ππ₯ ∫ π π₯ ππ₯ = π π₯ + πΆ π(ln π₯) = Notice that from the possible answers, the functions differ only by a constant. If we let C be any constant, then we may write ππ₯ π₯ π(sin π₯) = cos π₯ ππ₯ ∫ ππ₯ = ln π₯ + πΆ π₯ ∫ cos π₯ ππ₯ = sin π₯ + πΆ 4 π₯ +πΆ as the general answer. The function π₯ 4 + πΆ is called the antiderivative or the integral of4π₯ 3 . Antidifferentiation or integration is the process of finding the function whose derivative or differential is given. The symbol of differentiation π, and the symbol of integration ∫ are inverse to each other. What happens if π precedes ∫ or when it follows ∫ ? Let us suppose π(π₯) and πΉ(π₯) are functions whose relationship is given by ππΉ(π₯) = π(π₯)ππ₯ … (1) Your bright future starts here (075) 600 - 1507 | ucu.edu.ph San Vicente West, Urdaneta City, Pangasinan AdrianTomeldan@ucu.edu.ph | +63 917 9579 500 URDANETA CITY UNIVERSITY College of Engineering and Architecture Owned and Operated by the City Government of Urdaneta Integrating both sides of (1) gives ∫ ππΉ(π₯) = ∫ π(π₯)ππ₯ … (2) We have discussed in the preceding section that the process of finding the integral of a function π(π₯) requires our ability to guess another function πΉ(π₯) whose derivative is π(π₯) or whose differential is π(π₯)ππ₯. For example, we guess that From πΈππ (1.1) we see that ∫ π(π₯)ππ₯ = πΉ(π₯) + πΆ . Substituting this in (2), we have ∫ 3π₯ 2 ππ₯ = π₯ 3 + πΆ because π(π₯ 3 + πΆ) = 3π₯ 2 ππ₯. ∫ ππΉ(π₯) = πΉ(π₯) + πΆ … πΈππ (1.2) ο· Integrating the differential of a function gives that function plus an arbitrary constant. To reduce the amount of guesswork, basic integration formulas, are set up to facilitate integration. The first six formulas are given below. Note that the letters π, π, and πΆ are constants and π(π₯) and π(π₯) are differentiable functions of π₯. For example, ∫ π(π₯ 4 ) = π₯ 4 + πΆ ∫ π(tan π₯) = tan π₯ + πΆ ∫ π(π¦) = π¦ + πΆ ∫ π(π π₯ ) = π π₯ + πΆ 1) ∫ 0ππ₯ = πΆ 2) ∫ ππ₯ = π₯ + πΆ 3) ∫ πππ₯ = ππ₯ + πΆ π₯ π+1 4) ∫ π₯ π ππ₯ = π+1 + πΆ Next, we discuss when π precedes ∫ , By πΈππ (1.1) ∫ π(π₯)ππ₯ = πΉ(π₯) + πΆ if ππΉ(π₯) = π(π₯)ππ₯ Differentiating both sides of πΈππ (1.1), we get π[∫ π(π₯)ππ₯] = π[πΉ(π₯) + πΆ] = ππΉ(π₯) … (3) 5) ∫ ππ(π₯)ππ₯ = π ∫ π(π₯)ππ₯ Substituting equation (1), ππΉ(π₯) = π(π₯)ππ₯, in equation (3), we get π[∫ π(π₯)ππ₯] = π(π₯)ππ₯ … πΈππ (1.3) ο· Note: When π precedes∫ , they annul each other. 6) ∫ [π(π₯) ± π(π₯)]ππ₯ = ∫ π(π₯)ππ₯ + ∫ (π(π₯)ππ₯ For example, π ∫ 4π₯3ππ₯ = 4π₯3ππ₯ π ∫ π πππ₯ππ₯ = π πππ₯ππ₯ Proof: π(πΆ) = 0 β ππ₯ = 0 Proof: π(π₯ + πΆ) = ππ₯ + 0 = ππ₯ Proof: π(ππ₯ + πΆ) = π(πππ₯) + ππΆ = πππ₯ for any rational number π ≠ −1 Proof: π₯ π+1 1 (π + 1)π₯ π+1−1 ππ₯ π ( )= π+1 π+1 = π₯ π ππ₯ Proof: π(π ∫ π(π₯)ππ₯) = ππ ∫ π(π₯)ππ₯ = π π(π₯)ππ₯ Proof: π[∫ π(π₯)ππ₯ ± ∫ π(π₯)ππ₯ = π∫ π(π₯)ππ₯ ± π ∫ π(π₯)ππ₯] = π(π₯)ππ₯ ± π(π₯)ππ₯ EXAMPLE 1: 1.2 Basic Integration Formulas Your bright future starts here π 4+1 a) ∫ 5π₯ 4 ππ₯ = 5 ∫ π₯ 4 ππ₯ = 5 ( 4+1 ) + πΆ = π 5 + πΆ Formula (4) (075) 600 - 1507 | ucu.edu.ph San Vicente West, Urdaneta City, Pangasinan AdrianTomeldan@ucu.edu.ph | +63 917 9579 500 URDANETA CITY UNIVERSITY College of Engineering and Architecture Owned and Operated by the City Government of Urdaneta b) ∫ 4ππ₯ = 4∫ ππ₯ = 4π₯ + πΆ Let π’ = π₯ + 1, then ππ’ = ππ₯. Formula (2) c) ∫ 6(π₯ + 1)ππ₯ = 6 ∫ (π₯ + 1)ππ₯ = 6[∫ π₯ππ₯ + ∫ ππ₯] = 6[ π₯2 + π₯] + πΆ = 3π₯ 2 + πΆ 2 Formula (6) ∫ (π₯ + 1)4 ππ₯ = 4+1 + πΆ = (π₯ + 1)2 + πΆ = 1⁄5 (π₯ + 1)5 + πΆ Formulas (4) & (2) d) ∫ (3π₯ 5 − 4π₯)ππ₯ = ∫ 3π₯ 5 ππ₯ − ∫ 4π₯ππ₯ Formula (6) EXAMPLE 2. Evaluate∫ (2 − 3π₯)5 ππ₯. = 3∫ π₯ 5 ππ₯ − 4 ∫ π₯ππ₯ Formula (5) π₯6 6 (π₯ + 1)4+1 π₯2 2 = 3 ( ) − 4 ( ) + πΆ Formula (4) = 1⁄2 π₯ 6 − 2π₯ 2 + πΆ Formula (3)-(6) enables us to evaluate the integral of any polynomial. For instance, see example 2. SOLUTION: Let π’ = 2 − 3π₯, then ππ’ = −3ππ₯. Note that the given integral does not have -3 preceding ππ₯. But then -3 can be written preceding dx if we neutralize it by a factor that we write before the integral sign. Thus, our new integral will appear in the following manner. 6 (2 − 3π₯) ∫ (2 − 3π₯)5 ππ₯ = − 1⁄3 ∫ (2 − 3π₯)5 (−3ππ₯) = − 1⁄3 +πΆ = 6 = − 1⁄18 (2 − 3π₯)6 + πΆ EXAMPLE 2: ∫ 8π₯ 3 + 12π₯ 2 − 4π₯ + 5)ππ₯ = 8∫ 8π₯ 3 + 12∫ π₯ 2 − 4∫ π₯ + 5∫ ππ₯ = 2π₯ 4 + 4π₯ 3 − 2π₯ 2 + 5π₯ + πΆ ο· 1.3 The Power Formula To insert the needed constant legitimately, we must compensate for it by putting its reciprocal as a factor outside the integral. EXAMPLE 3. οΆ 7. ∫ π’ Proof: π [ π π’π+1 ππ’ = + πΆ, π+1 where π ≠ −1 π’π+1 1 (π + 1)π’π+1 ππ’ = π’π ππ’ + πΆ] = π+1 π+1 Note: The differential ππ’ in formula 7 is an exact or complete differential of the base π’. The exponent π is a constant different from -1. EXAMPLE 1. Evaluate ∫ (π₯ + 1) ππ₯. Your bright future starts here SOLUTION: Let π’ = π₯ 2 − 2π₯ + 3, then ππ’ = 2π₯ππ₯ − 2ππ₯ = 2(π₯ − 1)ππ₯ ∫ (π₯ 2 − 2π₯ + 3)4 (π₯ − 1)ππ₯ = − 1⁄2 ∫ (π₯ 2 − 2π₯ + 3)4 (2)(π₯ − 1)ππ₯ = 1⁄10 (π₯ 2 − 2π₯ + 3)5 + πΆ EXAMPLE 4. 4 SOLUTION: Evaluate ∫ (π₯ 2 − 2π₯ + 3)4 (π₯ − 1)ππ₯ 1 1 Evaluate ∫ tan2 3 π₯ π πππ₯ ππ₯. sec 2 3 π₯ππ₯. SOLUTION: (075) 600 - 1507 | ucu.edu.ph San Vicente West, Urdaneta City, Pangasinan AdrianTomeldan@ucu.edu.ph | +63 917 9579 500 URDANETA CITY UNIVERSITY College of Engineering and Architecture Owned and Operated by the City Government of Urdaneta 1 1 1 Let π’ = π‘ππ 3 π₯, then ππ’ = (sec 2 3 π₯) (3 ππ₯) . 1 1 ∫ tan π₯ sec 2 π₯ ππ₯ 3 3 ππ’ οΆ 8. ∫ π’−1 ππ’ = ∫ π’ = πΌππ’ + πΆ, π’ ≠ 0. u 2 Proof: π(πππ’ + πΆ) = 31 tan 3 π₯ 1 1 1 = 3∫ (tan2 π₯) ([sec 2 π₯] ππ₯) = 3 +πΆ 3 3 3 3 1 = tan3 π₯ + πΆ 3 EXAMPLE 5. ο· ππ₯ Evaluate ∫ (π₯+1) SOLUTION: Let π’ = ln π₯, then ππ’ = ln π₯ ππ₯ = π₯ Formula 8 states that the integral of any quotient whose numerator is the differential of the denominator is the logarithm of the denominator. EXAMPLE 1. ln π₯ Evaluate ∫ π₯ ππ₯ ∫ (ln π₯ ) 2 2 ππ₯ . π₯ 1 2 + πΆ = ln2 π₯ + πΆ SOLUTION. Let π’ = π₯ + 1, then ππ’ = ππ₯. Thus the given integral takes the form of ππ’ ∫ π’. ∫ EXAMPLE 6. Evaluate ∫ (1 + 4π −π₯ )(π −π₯ )ππ₯ SOLUTION. ππ₯ = ln(π₯ + 1) + πΆ π₯+1 EXAMPLE 2. π₯ ππ₯ Let π’ = 1 + 4π −π₯ , then ππ’ = −4π −π₯ ∫ (1 + 4π ππ’ π’ −π₯ )(π −π₯ 1 1 (1 + 4π −π₯ )5 ππ₯) = − ∫ (1 + 4π −π₯ )4 (−4π −π₯ ππ₯) = − +πΆ 4 4 5 1 = − (1 + 4π −π₯ )5 + πΆ 20 Evaluate ∫ π₯ 2 −3 SOLUTION. Let π’ = π₯ 2 − 3, then ππ’ = 2π₯ππ₯. π₯ ππ₯ 1 2π₯ ππ₯ 1 ∫ π₯ 2 −3 = 2 ∫ π₯ 2 −3 = 2 ln(π₯ 2 − 3) + πΆ 1.4 Extension of Power Formula π’π+1 The power formula ∫ π’π ππ’ = π+1 + πΆ is applicable for any rational number π except when π = −1. This is so because the power formula is undefined when π = −1. We now extend the power formula for the special case π = −1. Your bright future starts here EXAMPLE 3. π π₯ ππ₯ Evaluate ∫ 1+π π₯ (075) 600 - 1507 | ucu.edu.ph San Vicente West, Urdaneta City, Pangasinan AdrianTomeldan@ucu.edu.ph | +63 917 9579 500 URDANETA CITY UNIVERSITY College of Engineering and Architecture Owned and Operated by the City Government of Urdaneta SOLUTION. = ∫(π₯ + 1)ππ₯ + ∫ Let π’ = 1 + π π₯ , then ππ’ = π π₯ ππ₯. ∫ π π₯ ππ₯ = ln(1 + π π₯ ) + πΆ 1 + ππ₯ EXAMPLE 2. Evaluate ∫ EXAMPLE 4. (π₯ + 1)2 ππ₯ = + ln(π₯ + 1) + πΆ π₯+1 2 π₯ ππ₯ √1−π₯ SOLUTION. sec2 3π₯ππ₯ Evaluate ∫ 2+tan 3π₯ Rewrite π₯ as −[(1 − π₯) − 1]. SOLUTION. ∫ Let π’ = 2 + tan 3π₯, then ππ’ = (sec 2 3π₯)(3ππ₯) . ∫ sec 2 3π₯ ππ₯ 1 sec 2 3π₯ 3ππ₯ 1 = ∫ = ln(2 + tan 3π₯) + πΆ 2 + tan 3π₯ 3 2 + tan 3π₯ 3 π₯ ππ₯ √1 − π₯ = −∫ (1 − π₯) − 1 √1 − π₯ 3 1 1 ππ₯ = − ∫[(1 − π₯)2 − (1 − π₯)−2 ]ππ₯ 1 3 1 (1 − π₯)2 (1 − π₯)2 2 =− + + πΆ = − (1 − π₯)2 + 2(1 − π₯)2 + πΆ 3 1 3 2 2 1.5 Algebraic Manipulation In Differential Calculus, we are asked to differentiate functions or algebraic equations, and this can be done easily by simply applying the differentiation formulas. However, in integration problems, it is necessary in some cases to perform first certain algebraic manipulation to the integrand before an integration formula will apply. Common algebraic manipulation makes use of expansion or performing division in rational fractions. EXAMPLE 3. Evaluate ∫ ππ₯ 1−π −π₯ SOLUTION. Multiply both numerator and denominator by π π₯ . ∫ ππ₯ π π₯ ππ₯ π π₯ ππ₯ = ∫ = ∫ = ln(π π₯ − 1) + πΆ 1 − π −π₯ π π₯ (1 − π −π₯ ) ππ₯ − 1 EXAMPLE 1. EXAMPLE 4. π₯ 2 ππ₯ Evaluate ∫ π₯+1 (π₯+4)ππ₯ Evaluate ∫ (π₯+2)2 SOLUTION. π₯2 1 Performing division gives π₯+1 = π₯ + 1 + π₯+1. ∫ π₯ 2 ππ₯ 1 = ∫ (π₯ + 1 + ) ππ₯ π₯+1 π₯+1 SOLUTION. π₯+4 (π₯+2)+2 Rewrite (π₯+2)2 = (π₯+2)2 = Your bright future starts here 1 π₯+2 2 + (π₯+2)2 (075) 600 - 1507 | ucu.edu.ph San Vicente West, Urdaneta City, Pangasinan AdrianTomeldan@ucu.edu.ph | +63 917 9579 500 URDANETA CITY UNIVERSITY College of Engineering and Architecture Owned and Operated by the City Government of Urdaneta (π₯ + 4)ππ₯ ππ₯ 2 −2 ∫ = ∫ + ∫ 2(π₯ + 2) ππ₯ = ln(π₯ + 2) − +πΆ (π₯ + 2)2 π₯+2 π₯−2 SOLUTION. 1 Let π’ = πππ π₯, then ππ’ = −π πππ₯ππ₯ or − csc π₯ ππ₯ ∫ 1.6 Integration of Exponential Functions There are two basic formulas for the integration of exponential functions: οΆ ππ’ 9. ∫ π ππ’ = + πΆ, where π ln π π’ π’ π’ > 0 οΆ 10. ∫ π ππ’ = π + πΆ π cos π₯ ππ₯ π cos π₯ ππ₯ = −∫ = −π πππ π₯ + πΆ csc π₯ −csc π₯ EXAMPLE 4. 2+π −π₯ Evaluate ∫ ( π −π₯ ) ππ₯ SOLUTION. Formula 10 is a special case of formula 9, that is when π = π. Algebraic manipulation: 2+π −π₯ π −π₯ = 2π π₯ + 1 2 + π −π₯ ∫ ( −π₯ ) ππ₯ = ∫(2π π₯ + 1)ππ₯ = ∫ 2π π₯ ππ₯ + ∫ ππ₯ = 2π π₯ + π₯ + πΆ π EXAMPLE 1. Evaluate ∫ 2π₯ ππ₯. SOLUTION. 1.7 Integrals of Hyperbolic Functions Let π’ = π₯, then ππ’ = ππ₯. ∫ 2π₯ ππ₯ = 2π₯ +πΆ ln 2 EXAMPLE 2. Evaluate ∫ π −3π₯ ππ₯ SOLUTION. The six hyperbolic functions are: π π’ − π −π’ sinh π’ = 2 π π’ + π −π’ cosh π’ = 2 π π’ − π −π’ tanh π’ = π’ π + π −π’ csch π’ = sech π’ = coth π’ = 2 π π’ − π −π’ 2 π π’ + π −π’ π’ −π’ π +π π π’ − π −π’ Let π’ = −3π₯, then ππ’ = −3ππ₯. 1 1 ∫ π −3π₯ ππ₯ = − ∫ π −3π₯ (−3ππ₯) = − π −3π₯ + πΆ 3 3 EXAMPLE 3. π π0π π₯ ππ₯ Evaluate ∫ csc π₯ Your bright future starts here The derivatives of these functions are as follows: π π (sinh π’) = cosh π’ ππ’ (cosh π’) = sinh π’ ππ’ ππ₯ ππ₯ π π (tanh π’) = sech2 π’ ππ’ (coth π’) = −csch2 π’ ππ’ ππ₯ ππ₯ π (csch π’) = −csch π’ πππ‘β π’ ππ’ ππ₯ π (sech π’) = −sech π’ π‘ππβ π’ ππ’ ππ₯ (075) 600 - 1507 | ucu.edu.ph San Vicente West, Urdaneta City, Pangasinan AdrianTomeldan@ucu.edu.ph | +63 917 9579 500 URDANETA CITY UNIVERSITY College of Engineering and Architecture Owned and Operated by the City Government of Urdaneta Integrating these derivatives, we get the integration formulas for the hyperbolic functions. οΆ 11. ∫ πππ β π’ ππ’ = π ππβ π’ + πΆ οΆ 12. ∫ π ππβπ’ ππ’ = πππ β π’ + πΆ οΆ 13. ∫ sech2 π’ ππ’ = π‘ππβ π’ + πΆ οΆ 14. ∫ csch2 π’ ππ’ = −πππ‘β π’ + πΆ οΆ 15. ∫ csch π’ πππ‘β π’ ππ’ = −ππ πβ π’ + πΆ οΆ 16. ∫ sech π’ π‘ππβ π’ ππ’ = −π ππβ π’ + πΆ EXAMPLES: 1 1 1) ∫ sinh 2π₯ ππ₯ = 2 ∫(sinh 2π₯)2ππ₯ = 2 cosh 2π₯ + πΆ π₯ π₯ 1 π₯ 2) ∫ cosh ππ₯ = 3 ∫(cosh ) ππ₯ = 3 sinh + πΆ 2 3 3 3 π π₯ −π −π₯ 3) ∫ tanh π₯ ππ₯ = ∫ (π π₯ +π −π₯ ) ππ₯ = ln(π π₯ + π −π₯ ) + πΆ 1 1 4) ∫ sech 3π₯ tanh 3π₯ ππ₯ = ∫ sech 3π₯ tanh 3π₯ 3ππ₯ = − sech 3π₯ + πΆ 3 3 ππ₯ 5) ∫ csch2 (ln π₯) = − coth(ln π₯) + πΆ π₯ ππ₯ ππ₯ 6) ∫ sech2 √π₯ = 2 ∫ sech2 √π₯ ( ) = 2 tanh √π₯ + πΆ 2√π₯ √π₯ Your bright future starts here (075) 600 - 1507 | ucu.edu.ph San Vicente West, Urdaneta City, Pangasinan AdrianTomeldan@ucu.edu.ph | +63 917 9579 500