Question Detail

MTH 102 MTH 102 Past Questions Objective Question

Question

Evaluate ∫ dx / (x2 + 4x + 7).
Options
A <i>(1/&radic;2) tan<sup>-1</sup>((x+3)/&radic;2) + C</i>
B <i>(1/&radic;3) tan<sup>-1</sup>((x+2)/&radic;3) + C</i>
Correct Answer
C <i>(1/&radic;6) tan<sup>-1</sup>((x+7)/&radic;6) + C</i>
D <i>(1/&radic;5) tan<sup>-1</sup>((x+6)/&radic;5) + C</i>
Correct Answer

Option B is the correct answer.

Detailed Explanation

First, complete the square for the denominator: x2 + 4x + 7.x2 + 4x + 7 = (x2 + 4x + 4) + 3 = (x+2)2 + 3.The integral becomes: ∫ dx / ((x+2)2 + 3).This is in the form of the inverse tangent integral: ∫ du / (u2 + a2) = (1/a) arctan(u/a) + C.Here, u = x+2 (so du = dx) and a2 = 3, which means a = √3.Substitute these values:= (1/√3) arctan((x+2)/√3) + C.Note: arctan(x) is also written as tan-1(x).

Hint

Complete the square in the denominator and then use the standard integral formula for ∫ du / (u2 + a2).

Question Info