Question

Whats the first step that i should do with this integral? I tried to solve it by parts but i dont know what U should be.

Answer 1

\[\int\limits (x ^{2}+1)COS(x ^{3}+3x)\]

Answer 2

first decide which one you wanna make as variable, for example x2+1. then you solve the cos (x3+3x) integral

Answer 3

after finish, you make the cos (x3+3x) as variable, then finish x2+1 integral

Answer 4

u = x³ + 3x --> du = ...?

Answer 5

its differential. du=3x2+3

Answer 6

@Chef86 Hello...0!

Answer 7

@Chef86 Why don't you show up on your post instead of messaging?

Answer 8

\[dU = \frac{ SIN(x ^{3}+3x) }{ 3x ^{2}+3 }\]

Answer 9

dang i meant T

Answer 10

No, u = x³ + 3x --> du = ...?
( no sin, cos yet)

Answer 11

du = 2x^2 + 3

Answer 12

its 3x^2 +3

Answer 13

whoops i meant 3

Answer 14

3(x^2 +1)

Answer 15

\[\frac{ 1 }{ 3 } du\]

Answer 16

x^2 + 1 reminds me of the inverse of the tangent

Answer 17

meeen, its my first year calculus university, I've alrready forget >.<

Answer 18

NO, don't go over complicated !!!
u = x³ + 3x -->du/ 3 = ( x² + 1 ) dx
Just plug u and du in!

Answer 19

It's plain U-substitution!

Answer 20

i was trying to do it by parts before which is why i got confused by this

Answer 21

and i just put the sin in and its done basicly

Answer 22

sin(U) + c

Answer 23

So 1/3 ∫ cos u du = (1/3) sin u+ C
= (1/3) sin ( x³ + 3x) + C

Answer 24

thats what i got thks

Answer 25

Then why didn't you post it, instead of going around by Part, then U !!!

Answer 26

Im sorry that i even asked, i didnt mean to get you so angry.