Worked solution
Complete the square and match a standard integral
Find the following integrals:
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h) .
CJC · Discussion · Question 4
Answer
(a) .
(b) .
(c) .
(d) .
(e) .
(f) .
(g) .
(h) .
(a)
Factor out 9: . Apply the logarithmic formula with . The coefficient is .
The integral is .
(b)
Complete the square: . Apply the difference-of-squares logarithmic form.
The integral is .
(c)
The denominator is . Use the form with , retaining absolute values.
The integral is .
(d)
Factor 2 and complete the square: . Integrate as . The logarithm coefficient is . Multiply numerator and denominator of its ratio by √2 to get the printed form.
The integral is .
(e)
Complete the square to . Apply the arctangent form with u=x+2 and a=4.
The integral is .
(f)
Complete the square: . The printed formula box matches , and . Multiply and divide the integral by √2 to match . Simplification gives the stated coefficient 2/√71 and argument (4x+3)/√71.
The integral is .
(g)
The radicand is . Apply the inverse-sine form. The original integrand requires −5<y<1.
The integral is .
(h)
Factor √9 from the denominator to obtain . The result is , with −5/3<x<5/3.
The integral is .
Common mistakes
A square-root denominator leads to an inverse-sine form; the same quadratic without a square root can require a logarithm.