/sci/ - Science & Math

[OP !nBbTYMQPIs No.5739041]

how can you do this using substitution?

i've tried it with u = (x+4)^(9/2) but failed

is that the correct u value?

perhaps, i fucked up in the process somewhere, but i can't seem to figure this fucker out.

[Anonymous No.5739050]

Just take u=x+4. du=dx and u-4=x.

[OP !nBbTYMQPIs No.5739056]

>>5739050
thanks, i was able to do it with that u value

my biggest problem with integrals like this is picking the correct u value.

how do you do this best? is it just a matter of practice practice practice to sort of gain an "ability" with being able to pick correctly?

[Anonymous No.5739067]

Here

[Anonymous No.5739070]

It takes a lot of practice, however there is a tip that may help you figuring out what substitution will solve the problem. When making a substitution u=f(x), see if the derivative f'(x) also appears in the integrand (sometimes you have to manipulate the integrand to achieve this).

[Anonymous No.5739071]

>>5739056
Not him but yes, there's not a good substitute for just practicing until you've seen different types of problems.

Also don't be afraid to just say fuck it and try something.
No point sitting there staring at the problem when chances are it's not nearly as complicated as you want to make it. If you know you're supposed to use substitution, just pick something, differentiate it, and then see what you can do.
If it's an absolute nightmare, try something else because you probably picked a poor substitution.

Nobody says you have to get it right with your first pick, and you'll probably wind up either choosing right or seeing a better option.

[OP !nBbTYMQPIs No.5739073]

>>5739067
that is a way cleaner way of doing it then what we learned in class.

i literally would never have thought to make u=(x+4)^(1/2)

>>5739070
>>5739071
alrighty, i'll have to hit the textbook and spend the rest of the day doing practice problems

thanks for the help all

[Anonymous No.5739090]

Just do that shit by parts, takes about 20 whole seconds