# data[].attributes.body
I would say that the one integration rule that sticks out as being the most difficult for me would be #20. I struggle with quite a few and really the only solution is more practice. It takes time and practice to retain the concepts. I will agree that the trig rules can get tricky because I still have to reference the formulas because I have yet to memorize them.

# data[].attributes.body
I seem to struggle with #20. For me it seems to me more difficult to remember the rule. I also have a hard time remembering to use arcsec. I need to find a key to using du and the integral. This one just hasn't made sense to me yet.

# data[].attributes.body
#18
I sometimes have trouble with things that involve #18 because sometimes the integrand involves factoring something out of a radical

# data[].attributes.body
I had a pretty difficult time with Calc II. Remembering many of the functions was somewhat difficult. I'm actually going over many of these functions again being that I took a break from Calc and took a discrete mathematics course. These two links will definitely be helpful with refreshing myself with integrals and I'm brushing up on my trig functions as well.

# data[].attributes.body
I, like Matt, struggle with most of the trig rules. Rules, 12-20 I always have to look up.  I'm sure that is because my trig is pretty weak.  It's gotten better through calc 1 and 2 but nothing involving trig is intuitive for me and I always have to do research and look things up to make sense of it.

# data[].attributes.body
I struggled with #18-20 because I did not always recognize the pattern when additional work was needed to complete the square.

# data[].attributes.body
I did, jacob mason.

# data[].attributes.body
Matt, there should be a pull-out card in the front of your textbook with some of the formulas you need on it. See http://tutorial.math.lamar.edu/pdf/Calculus_Cheat_Sheet_Integrals.pdf
Even better is
https://mslc.osu.edu/sites/mslc.osu.edu/files/Integral%20Calculus%20Formula%20Sheet_0.pdf
See also appendix B starting on p. A3.

# data[].attributes.body
Who wrote about #18? I need a name so I know whom to give credit.

# data[].attributes.body
I usually have trouble with # 18,19 and 20, I get lost in the process and make mistakes. Yes, I am still in he process of mastering them.

# data[].attributes.body
I struggled with #19.  One struggle was recognizing when to use the integral.  Then there are the times when du needs to be manipulated or a and u are not perfect squares.  I still struggle with this integral.

# data[].attributes.body
Honestly, I've struggled with pretty much all of them. The ones I struggle with the most though are the trig rules. Mostly because it's not as simple as "adding 1 to the exponent" or "divide by the nat. log ". These require you to remember the formula, (integral of sin u = -cos u, etc). Naturally it would seem this should be easier because the formula is given but since they're not numeric values my brain probably doesn't think "math". To get around this I've created notes and flashcards to help with these trig rules. I wish I new this table existed in Calc 2, I would have printed it off!

# data[].attributes.body
I always have trouble with #20 and still have to look it up. Yes, after all these years.