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

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lgbasalloteBest ResponseYou've already chosen the best response.1
take the derivative of u....if that du is present in the integrand you can use sub
 one year ago

satellite73Best ResponseYou've already chosen the best response.1
don't use them on saturday night. go out and party
 one year ago

lgbasalloteBest ResponseYou've already chosen the best response.1
wait...we're talking about usub right? not algebraic sub?
 one year ago

malexanderBest 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.
 one year ago

lgbasalloteBest ResponseYou've already chosen the best response.1
go out and integrate?
 one year ago

lgbasalloteBest 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...
 one year ago

satellite73Best ResponseYou've already chosen the best response.1
a function multiplied by something that is either the derivative, or a constant multiple of the derivative
 one year ago

satellite73Best 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
 one year ago

satellite73Best ResponseYou've already chosen the best response.1
should have been \[\int f(g(x))g'(x)dx\]
 one year ago

lgbasalloteBest ResponseYou've already chosen the best response.1
^integral of the chain rule
 one year ago

marcoduuuhBest ResponseYou've already chosen the best response.0
Don't use it on Sundays either, yolo.
 one year ago

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

malexanderBest ResponseYou've already chosen the best response.0
Why those @lgbasallote ?
 one year ago

lgbasalloteBest 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
 one year ago

lgbasalloteBest ResponseYou've already chosen the best response.1
2d is usubbable too
 one year ago

malexanderBest ResponseYou've already chosen the best response.0
Oh 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)
 one year ago

lgbasalloteBest ResponseYou've already chosen the best response.1
integrating 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
 one year ago

lgbasalloteBest ResponseYou've already chosen the best response.1
also 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
 one year ago

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

malexanderBest 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...
 one year ago

lgbasalloteBest ResponseYou've already chosen the best response.1
i see...so you're just learning usub...try integrating the ones i said..2b and 2d
 one year ago

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

lgbasalloteBest ResponseYou've already chosen the best response.1
new post...im too lagged for a long thread lol
 one year ago

malexanderBest ResponseYou've already chosen the best response.0
LOL! ok sounds good
 one year ago
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