Answer
Use substitution with $u=9x^2$.
Work Step by Step
Given $$ \int x \cos \left(9 x^{2}\right) d x$$
Let
$$u = 9x^2 \ \ \ \ \ du =18x $$
Then
$$\int x \cos \left(9 x^{2}\right) d x= \frac{1}{18} \int \cos udu $$
Calculus (3rd Edition)
by Rogawski, Jon; Adams, Colin
Published by
W. H. Freeman
ISBN 10:
1464125260
ISBN 13:
978-1-46412-526-3
Chapter 8 - Techniques of Integration - 8.1 Integration by Parts - Exercises - Page 396: 74
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