Worked solution
Ten direct integrals and reverse chain rules
Find the following integrals:
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
(j) .
CJC · Discussion · Question 3
Answer
(a) .
(b) .
(c) .
(d) .
(e) .
(f) .
(g) .
(h) .
(i) .
(j) .
(a)
Expand the integrand as and integrate each power: . The square root restricts the original real input to .
The integral is .
(b)
The square expands to . Integrate term by term. The original reciprocal square root requires , so the printed is also on that domain.
The integral is .
(c)
Insert the inner derivative: . The reverse chain rule gives .
The integral is .
(d)
View this as and use the derivative of ln x. The real input requires x>0.
The integral is .
(e)
Rewrite . Integrate the constant and account for the inner derivative −1 in the logarithmic term; t≠1.
The integral is .
(f)
Rewrite the numerator as , the differential of ln x. Apply the logarithmic rule to ln x; the original domain is x>0, x≠1.
The integral is .
(g)
The numerator differentiates the denominator. The source first uses and then removes the absolute value because eˣ>0 for every real x.
The integral is .
(h)
Write the integral as . The reciprocal factor is the derivative of √x; x>0.
The integral is .
(i)
Write and use the derivative of 1/x. Retain x≠0.
The integral is .
(j)
For base 2017 the derivative includes both ln2017 and the inner derivative 2017. Divide by both factors.
The integral is .
Common mistakes
Retain absolute values in logarithms unless the original domain makes the argument positive.