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malexander
 3 years ago
Hi. I wanted to know how does one know when to use the substitution rule for integrals and when not too?
malexander
 3 years ago
Hi. I wanted to know how does one know when to use the substitution rule for integrals and when not too?

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lgbasallote
 3 years ago
Best ResponseYou've already chosen the best response.1take the derivative of u....if that du is present in the integrand you can use sub

satellite73
 3 years ago
Best ResponseYou've already chosen the best response.1don't use them on saturday night. go out and party

lgbasallote
 3 years ago
Best ResponseYou've already chosen the best response.1wait...we're talking about usub right? not algebraic sub?

malexander
 3 years ago
Best ResponseYou've already chosen the best response.0@lgbasallote yep I am. I wanted to know when you look at an integral problem, how do you know to use either usubstitution or not.

lgbasallote
 3 years ago
Best ResponseYou've already chosen the best response.1go out and integrate?

lgbasallote
 3 years ago
Best ResponseYou've already chosen the best response.1@malexander it involves mastery of derivatives...if you know many derivativves you can see them immediately...if not..you can try uing then derive it...

satellite73
 3 years ago
Best ResponseYou've already chosen the best response.1a function multiplied by something that is either the derivative, or a constant multiple of the derivative

satellite73
 3 years ago
Best ResponseYou've already chosen the best response.1\[\int\sqrt{x^3+3}x^2dx\] for example, because the derivative of \(x^3+3\) is \(3x^2\) and what i wrote above was wrong

satellite73
 3 years ago
Best ResponseYou've already chosen the best response.1should have been \[\int f(g(x))g'(x)dx\]

lgbasallote
 3 years ago
Best ResponseYou've already chosen the best response.1^integral of the chain rule

marcoduuuh
 3 years ago
Best ResponseYou've already chosen the best response.0Don't use it on Sundays either, yolo.

malexander
 3 years ago
Best ResponseYou've already chosen the best response.0Your confusing me @satellite73. Um. Lets say you have these four integrals (question 2). In this question, which one would you need usubstitution and why?

malexander
 3 years ago
Best ResponseYou've already chosen the best response.0Why those @lgbasallote ?

lgbasallote
 3 years ago
Best ResponseYou've already chosen the best response.1\[\large \int \frac{3x^3}{\sqrt{x^4 + 1}} = 3\int \frac{x^3}{\sqrt{x^4 + 1}}\] if i let u = x^4 + 1 du = 4x^3 the constant 4 is not important...but x^3 is...and it is present in the integrand so you can use usub

lgbasallote
 3 years ago
Best ResponseYou've already chosen the best response.12d is usubbable too

malexander
 3 years ago
Best ResponseYou've already chosen the best response.0Oh okay. That makes a bit more sense @lgbasallote . However, I thought we were not able to integrate fractions? (Im a cal 1 student, maybe inter grating fractions is in cal 2)

lgbasallote
 3 years ago
Best ResponseYou've already chosen the best response.1integrating fractions....for example 1/u^2 1/u^2 = u^(2) according to basic algebra according to basic integration...you can use power rule on that..i assume you're familiar with that note: NEVER use power rule on 1/u <the integral of that is automatically ln u

lgbasallote
 3 years ago
Best ResponseYou've already chosen the best response.1also note that i am using u...this is because u is a function of x meaning it is an expression..not limited to only a variable

malexander
 3 years ago
Best ResponseYou've already chosen the best response.0right, i remember that @lgbasallote about 1/u^2..and also thats fine, we use "u" in class

malexander
 3 years ago
Best ResponseYou've already chosen the best response.0@lgbasallote ln is in calc 2, so i hope i get to do that next semester hehe...i think i just need to do more problems with integration then...

lgbasallote
 3 years ago
Best ResponseYou've already chosen the best response.1i see...so you're just learning usub...try integrating the ones i said..2b and 2d

malexander
 3 years ago
Best ResponseYou've already chosen the best response.0thanks again @lgbasallote ....i have another question...do u mind me asking it here, or posting another question box?

lgbasallote
 3 years ago
Best ResponseYou've already chosen the best response.1new post...im too lagged for a long thread lol
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